Sorry to hear that happened. I personally don't keep my gates open unattended unless I'm on local play with my husband. That way he can come and go as he pleases. My flower giveaways are also delivery only for the reason you stated above.
Still not as bad as years ago, when ACNL first came out, the grifers were horrible! It was impossible to know who to trust. There is at least more good people than there are bad these days, but it's still sad to see these things still going on.
I was going to for train station visits due to timezones and such, but the person then had other things to be doing. Really depends on your town status and if there's much to mess up. Also, if there's only one person on your friends list, then you know who did the damage if there is any.
On another note, Enders, just how frequently are you getting suspended from this site? It's crazy how often your username goes brown, lol.