I've complained before about the ways Spamton is commonly mischaracterized in fanon, and how the characterizations he's given are pulled out of nowhere, or clearly just come from people projecting how they would write the embodiment of spam mail onto him instead of actually paying attention to how he's written.
The interesting thing is that, as an ad, Spamton theoretically should be like some of those fanon mischaracterizations.
Ads often promote garbage. Their purpose is to mislead people and rip them off by convincing them to buy a bad product. They're supposed to only care about their profits, not their customers, though they may pretend like they care about the customer as a sales tactic. They're meant to be predatory and greedy, restrained mainly by the confines of law and by how much they could realistically convince a customer to pay.
The Addisons follow that purpose pretty closely. They advertise bad products and successfully trick people into buying, and they do so shamelessly. Their top priority being profit is further evident in their treatment of Spamton, who they left to fend for himself because he was "bad for business", despite being well aware that he would be unable to stay afloat without outside help. Even if they pity him, their profits matter more.
But Spamton... He's different.
We don't know what he was trying to sell back when he was an unsuccessful Addison, but we know of one product that he used to sell during his successful era: B.ShotBowtie. It's a good Armor, and its good quality is further emphasized by the fact that Swatch is still selling it a decade later. The bow tie being a good product, and the lack of any bad products attributed to Spamton in that time period, suggests that he was likely selling decent or even good products generally. And it's not like being successful would preclude him from being a shameless scammer; there are plenty of people getting rich through scamming. No, this is a matter of principle for him. He does not want to scam. It took him becoming homeless and lacking any resources outside of what he can dig out of a dumpster to resort to scamming as a means of survival.
In fact, he may not even want to be a salesman. As a Darkner, he can't completely opt out of being an ad, as his purpose dictates he must be, but he bent the rules as far as he could. Through his relationship with Tenna, he discovered a love for entertainment, and he has learned to perform the same way Tenna does; note their similar manners of speaking. The contract the two of them signed, along with obliging Spamton to share his secret with Tenna, is also implied to make them co-hosts on TV Time. While the show was still going to include sales, or at least some kind of deals, due to the inability for Spamton to abandon his purpose, it was going to be secondary to his preferred job of being an entertainer like Tenna.
Although the job of an entertainer does come with fame and money, it's worth noting that it revolves around pleasing an audience. The job of a salesman is to extract money from the customer and doesn't require a positive contribution to the customer's life, while an entertainer works for the audience and has to make them happy. You can trick a customer into buying a bad product, but you can't really trick an audience into enjoying a bad show and continuing to give it money.
Speaking of the contract, and of Spamton's intended job as Tenna's co-host...
Spamton knowingly took a big risk to make this commitment to Tenna. The contract cost him the support of his benefactor, which resulted in a swift end to his career, but this wasn't what made him turn on Tenna; it was Tenna not answering his calls and seemingly throwing away the commitment they had made to each other. That commitment was what mattered most to him, a commitment which also came with the promise of stability even if he lost his income. If he could have stable housing, food, etc. without that income, the loss of money didn't bother him all that much.
There's also the fact that he wanted to be Tenna's co-host, sharing the spotlight with him and, because of how the Dark Worlds work, being unable to ever surpass Tenna even if he tried, since Tenna is the ruler of TV World. Even if Tenna personally treats Spamton as an equal, the magic of the Dark World dictates that Spamton can never be on the same level, at least certainly not in TV World. If Spamton's goal was a shallow pursuit of fame, he would hate the idea of sharing it or being equals; he would want to be at the top. He would see Tenna as a competitor and would likely resent him, even if he found him physically attractive. But no, he loves Tenna. Deeply. And he loved the idea of sharing the spotlight as equals. This is the future that was taken from him, and that he was upset about losing.
Having spent a decade homeless and living off trash, completely abandoned by the society around him, he resorted to desperate measures to try to escape the Dark World, trying to steal Kris's SOUL. When that failed and he calmed down, he gave up on the escape attempts, but his hope in the goodness of others and his ability to have real friendships was restored, and he actively expressed a desire to help the Fun Gang break their own strings, turning himself into an object in order to do so. While he does somewhat benefit from this, no longer having to be in a dumpster, the party ultimately benefits more. He also gets upset if the inventory is full and he can't immediately add himself to it; he gets very attached to people and, given his history, is sensitive to rejection (real or perceived).
In many ways, Spamton has been shown to value reciprocity, fairness and commitment, to like being treated as an equal rather than a superior, and to care about others and want to genuinely make positive contributions to people's lives... And all of this is directly against what he's "supposed" to be, and is incredibly important to his story as someone who kept defying his purpose.
...Which makes it all the more frustrating when people ignore all that in favor of making him a shallow greedy scammer. It takes the purpose he rebels against as representative of who he is, completely ignoring that his whole story revolves around him trying to break free from it, and being at least partially successful.