nobody's ever stolen from me, mostly because i'm super careful with keeping my eye on people when they come over, but i have two shady accounts:
1) somebody came over for signatures, and i lead them through town to my villagers (to be safe ofc- i didn't expect them to do anything bad, it is just how i keep an eye on any player that comes through town), and after he was done, he asked if he could have a tour. i try to be chill and nice to people i'm wifi-ing with (of course! haha), so i said sure, and told him to follow me. while i was showing him around town, he picked up a lucky clover, but picking up lucky clovers is so heckin slow that OF COURSE i saw him do it, and i just turned around and looked at him. he put it down right away, and said "oops sorry, i accidentally picked it up" and so i was like "ok" (but inside, i was like "gotta get this scrub outta town soon"). a couple minutes later, he picked another clover up while i was farther ahead of him, but i doubled back bc i noticed he was out of sight and caught a glimpse of him holding that lucky clover high in the sky. he saw me double back, so he put it down, but i was getting salty (it was pretty obvious he was just trying to take them). i pretended like i was still chill and quickly wrapped up the tour and sent him home. thanks to my hovering skills, i didn't get robbed that day :')
2) this was just yesterday, actually! and not nearly as shady as the first guy... but i was having a small "visit etoile's rv" giveaway, and only letting people in 1 at a time. i let the girl who properly requested to come in, and after i lead her to the trailer park, i sat down on one of the log benches there, and suddenly the "someone is arriving" banner came up. i panicked at first bc ???? who???? so i decided to not cut the wifi and instead try to run to the station once the saving and arrive sequences were over to see who it was. i memorized the name and town of the visitor, and when they arrived, i ran over and asked who they were on tbtf. they said a username that i vaguely recognized, so i was like "oh ok," but then i had to take my attention off the newcomer to send off the girl who was legitimately visiting. while i said goodbye to the original visitor, the newer one zoomed around near the station and i lost sight of her a couple times. (as you can imagine, i was panicking, like "why is she here? is she taking stuff?") and then the newcomer visitor ran back into the train station and started going home. i was really nervous bc they might have taken stuff, but i didn't want to be a nuisance to the girl who legitimately was supposed to be in my town and had ordered stuff from etoile, so i let them both leave, knowing i had the tbtf username of the 2nd girl. when both were gone, i did a quick run-through of my town, checking for missing hybrids. i didn't think any were missing (and as of now, i still don't THINK any are), but i was kind of salty bc they came without an invitation. i checked the list of online forum users to see if the username the visitor gave me was still online, but they weren't. after doing some sleuthing (basically just googling "bell tree forums [mayor name] [town name]" i found the actual visitor. she gave me a different username, so that made me even saltier- but i just left her a casual vm asking if it was her who came over. i'm keeping her actual username a secret bc even though it wasn't cool of her to come over uninvited like that, i don't want people to avoid her- i don't think she actually took anything, just left a weird message on my bulliten board. she may see this, but uhhh i don't really care bc it scared me a lot and it wasn't that kind of her, given that so many people care a lot about their towns and don't appreciate random drop ins who lie about who they are....
anyway! those are my two traumatic experiences! i seriously don't think there are many people who steal, but always remember to stay safe and take precautions! make sure you can see everyone in your town at all times- this is easier if you only have one person over! and make sure to communicate with any rules you have in town!
hope nothing this scary ever happens to you again! it's not very nice for people to do ;;;