As a true crime buff, Dahmer was actually quite attractive, so much so that he had this huge fan club who worshipped him after he got caught, so many serial killer groupies.
You've gotta remember we're talking 78-early 90s, back when meeting another gay guy was extremely difficult, your only options were bars or cruising toilets. Bad smells were the least of your issues and some unassuming attractive blonde geek is not gonna raise too many red flags and if you're really drunk and tells you his fridge is malfunctioning,you're probably gonna believe him and try get off and get out as quickly as possible. You're either thinking with your dick orrrr he's paying you and your desperate. Either way he doesn't register as a threat.
Also, you can't go to the cops cos they'll either beat you up or do sfa.
There's a great scene in the first or second episode where the cops thought they might have caught aids by breathing in the same air as two gay men and needing to go shower.
I don't think Jeffrey would have raised any red flags with these people until it was too late and honestly from stories, being gay back then, if you wanted to have sex with someone, you were often doing it in gross dirty smelly secret places like abandoned houses, toilets.