Story arc: Bustin' Out
As previously mentioned, you can first meet Giuseppi at the beginning of The Sims: Bustin' Out. We've already described the situation of our first meeting with him from the point of view of our character, but let's spin that around and think about what that must have been like for Giuseppi.
He's in a dive bar for bikers in the shitty town of SimValley. He's standing around the empty arcade area, notably not playing any arcade games, just observing the scene, keeping his ears and eyes open for anything interesting, maybe enjoying a coke. This girl he's never seen before walks into the biker bar. She's clearly out of place here. But then she goes up to the owner, and sells him a ratty couch. Interesting, he thinks. Then she turns around, and notices him, a shady guy with leather jacket and black gloves and a thief cap. She makes a beeline for him, and he answers her greeting with his usual shtick, probably already somewhat surprised that this is happening at all - is she brave, or just stupid? But then, she replies by flirting with him. In a kinky way. She likes leather, and she's telling him that. As the very first thing she says, after her name. She basically lands on his lap. We imagine Giuseppi nearly has ice cubes come out his nose. He gathers his composure enough to flirt back, but mostly, he's amazed.
Imagine the life he's had until now. He's shady. People in town suspect him, and they're right. Does he have friends? He doesn't seem to. Why would anyone approach him? He looks so scary. But the main character does. If this story was told from Giuseppi's point of view, she'd be the manic pixie dream girl!
We infer that Giuseppi is not native to SimValley. Since he lives out of his van, he moves from place to place, and he moves on when there's no more "business" to do in a given town, usually pursued by cops. By when Bustin' Out happens, he seems to have been in SimValley for a while, but not too long. Everyone knows who he is, and that he has a moving service, and that he can help you move your furniture. Some people are starting to suspect him, but the police haven't quite caught on yet. But they are starting to. At the beginning of the game, Detective Dan D. Mann tasks the player with participating in an auction, because he suspects that there might be a crime ring in town, and he wants us to report if we see anything suspicious. We do as he says, but, in spite of Giuseppi's presence, we don't see anything odd. Detective Dan tells us to keep paying attention, because he's sure that crime is afoot.
And, sure enough, it is. When we move from Uncle Hayseed's barn to our first apartment in the clocktower, Giuseppi helps us move our stuff with his wonderful crate... we thank him, but he thanks us more. Later, after we return home from whatever we were doing, we get a notice that we've been robbed, which includes the face portrait of the burglar. He's wearing a mask, but it's obviously Giuseppi. He made off with our bed, which we suppose he scoped out as the most valuable object in our possession while he was helping us move.
So, there might not be an entire crime ring, but there is certainly a burglar in town.
At night, we can find him near the docks, selling his wares out of his van. You can get really good prices from him. You could say that his prices are a steal.
Later in the plot, we do a mutually beneficial quest with him. He helps us find the blueprints to the sewer system running under SimValley, and now we both can use the sewer system as a shortcut through town, by going down the manhole covers and popping up somewhere else. When we're in the sewers, we can even sometimes see him creeping along down there.
During this quest, Giuseppi informs us that there is a trapdoor in our apartment, which is where the blueprints are stored. We guess he noticed while he was helping us move, because he's the sort of person who would notice something like that. He ribs us a little for having not realized that the trapdoor was there earlier. Gameplay joke: the trapdoor wasn't there before.
It was around this part of the game when we purchased a burglar alarm, which prevents Giuseppi from robbing you. Even without it, it's important to note that Giuseppi won't rob you if you are at 100 relationship with him. Which we were. Our relationship with him had grown in the meanwhile, and there had been a lot of kissing and banging involved. He's no longer breaking into our apartment, because he's been breaking into us directly.
Some time passes, we have our adventures in town, and we move up in the world. We eventually go to live in the summer mansion of local bajillionaire Daddy Bigbucks. Giuseppi is still helping us move, and he can't help but notice where we're moving to, and wonders how are we able to afford this.
Here, you have the choice to answer that yeah, we're loaded, or reply to him more evasively. In either case, Giuseppi figures that the money must come from our Uncle Hayseed. At this point of the game, you might not necessarily be best friends with him as we were, but he's still observant enough to work out our family situation, and smart enough to understand that we can't be independently wealthy, which is indeed true - we're staying in this mansion because we did a favor for Daddy Bigbucks; we couldn't really afford it.
After this, our band mate Vera Vex tells us that her guitar has been stolen. She's sure it was Giuseppi, and wants us to bring him to justice and recover the guitar, and end his crime spree once and for all. We talk with Detective Dan, and he suggests that we use a camera to catch Giuseppi in the act and have proof of his crimes. We buy a camera, but we don't want to catch Giuseppi... We're hoping there's some twist to this plotline where we can get back the guitar while not betraying him.
The next time we visit Uncle Hayseed, however, we learn that the situation has escalated. Since Giuseppi thinks our uncle has a secret stash of money, he's now here to find it, and to get Uncle Hayseed to talk. Considering the stash doesn't exist, Uncle Hayseed couldn't tell him where the stash is, and, presumably, Giuseppi was amplifying his interrogation techniques. We find Uncle Hayseed tied to a chair, Giuseppi making away with all the furniture... and a guillotine in the bathroom. As much as we love Giuseppi, we need to save Uncle Hayseed. We use the camera's flash to stun Giuseppi, and he's apprehended and brought to jail, where he spends the rest of the game.
Thus ends Giuseppi's criminal career. For the rest of the game, he's in jail, and we can't talk to him. We've read other people say that sometimes he'll come close enough to the bars to talk with you, but we didn't get that in our game - maybe the nature of our relationship with him made him feel too betrayed.
While we see how the guillotine was likely just an interrogation technique, and Giuseppi probably never really intended to use it, it still seems extreme for him, to the point of being out of character. Until then, Giuseppi had only stolen the occasional single item from us, always when we weren't there, and clearly meaning us no physical harm. Here, he's needlessly escalated the situation with Uncle Hayseed. For what purpose? Without the guillotine, if he's caught, he's only convicted of stealing. With the guillotine, it's attempted murder. Why would he go all the way up to attempted murder, and to get what out of it? How much money could Uncle Hayseed have to even make this worthwhile? What was he planning to do afterwards? He must have been planning to immediately skip town, because there's no way that he can casually go about his day after that.
Anyway, at the end of the game, when the player character is revealed to be an alien and is about to go back to space, Giuseppi is temporarily let out of jail for the send-off party. From this experience, he definitely knows that maybe aliens exist.
...But our character crashes back to Earth, and our adventures pick up again in The Urbz.