I don't particularly care. I know the way it's done is pretty random but I like to think of it as their personalities showing through, with what sort of items and clothes they like if given the chance. I'm not as picky with the villagers I plan on keeping though I'll also spam them with gifts that would look cool and try to keep it looking relatively nice. I'm still trying to figure out how to get them to get rid of having so many clothes displayed, especially ugly clothes that wouldn't suit them at all and which they never wear... I'd send them chairs but I'm afraid they'll just swap them out with the clothes I do like on them.
With the rest of them, their houses are relatively intact. I haven't compared them to the originals very much and don't bother checking up on them a lot but I think the differences are very minor, if there are any. This is because I wouldn't want whoever got them next to get a completely ruined house. I don't do anything in particular to keep it that way, I'm just lazy and bad at finding things, deny some trade requests, and have swapped out the stuff in Re-Tail with overpriced food. I do agree to certain requests from some of them if I think it would be fun but that's about it.
I actually kind of want to make the homes of the ones I plan on keeping more personal and change up their usual themes but I suspect I'd probably just end up ruining everything completely.