Wait, why do you think that?
Fett isn't some expert on Han's life. This is what Fett knows: Han is a scoundrel, smuggler, and criminal who owes Jabba money and fled rather than pay. It's not like Jabba is going to offer more information than that, and Fett has no reason to ask any further questions (straightforward deadbeats like that are probably his bread-and-butter.)
It's not good, but I don't see how it's evil? Han isn't, like, some starving widow who fell into debt due to circumstances. (We see him give Jabba some excuses, but honestly given who Han is and his general reputation, both Jabba and Fett could entirely reasonably conclude that Han is simply stealing from them.)
Gannji and Enor seem similar. Yeah, they don't ask many questions, but as far as they know Elan is a wanted criminal (wanted for murder!) Like... supposing they'd actually gotten the right guy, and successfully brought in Nale. Would that be an evil act? Nale was, in fact, guilty of everything the poster said he was.