I have only lifted Architecture. Bug spray has not been reinvented. Someone knocked my Sim's trashcan over for some unknown reason and they have roaches. I know I can't have my Sims spray them or hire an exterminator. But a friend walked by and rang the doorbell and got greeted. First thing he did was spray cockroaches. Do I need to keep the friend from doing that or is it allowed?

I've never seen an visitor to a lot spray cockroaches, so this is a first.

That's a hard one too, but I think if you can't control them, it's okay. I guess you can indirectly control them by distracting them with your playable Sim, but I don't know... I think just go with what you're comfortable with.

I'm pretty sure this is allowed as long as you didn't tell them to do it.

And very handy I could do with a visitor doing that in my current challenge

If it's autonomous behavior from a visitor, you are in no way able to control them without cheating, so no, you don't lose points or lose the challenge, because of it.

However, it would be somewhat cheaty to specifically invite over the neatest sims, specifically hoping they'll spray the bugs. Although, if you get a very neat sim die from the roach-flu, and have their ghost come back and spray the bugs, you should probably get bonus points for that!

I have had ghosts clean house for me. I love it. But I have yet to see a ghost see roaches.

Oh, if you have Apartment Life, here's a trick: Put a garbage chute at your entry way, and whenever someone kicks over the can, see if you can get your sims to put the trash pile in the garbage chute, instead of standing the can upright. If you can get them to do that, then they'll leave the empty can kicked over, and you won't have to worry about roaches again, until some neat-nik stands the can up, autonomously.