Had the same problem. I love my baby girl with all my heart, but there was an adjustment period for both of us when we started to live together. She doesn't have streetsmarts of any kind. Shit like leaving her credit card on the passenger seat of her car and crying foul when someone breaks into her car and steals it. She wasn't happy when I told her point blank not to keep shit like that laying around in her car but tough titty, them the breaks. She learned her lesson after that. I don't know about you guys, but it's a pretty well know thing that sometimes, not saying always, but sometimes a salesman or repair person will "case" a house they will later rob by attempting to go there on business.
Personally, if there's a repair person inbound we let the other know so that the other isn't caught off guard. We don't let random door-to-door salsemen in our place. As far as her buying shit...if it's her money and the bills are paid she can buy whatever shit she wants. I won't bitch at her for buying magazines, she won't bitch at me for buying Skyrim. Fair deal to me, lmao.
My suggestion: Be fucking real with her. Stand your ground like a man and let her know how YOU feel about the shit. My view is, if I'm trusting your with thousands upon thousands of dollars of my personal property then you gotta respect that and I'll respect your shit. Don't change if you're right. Inviting some random dude into your home as a female and you're alone is fucking dumb. Hell, I can handle myself and I only crack the door.
All the people saying nothing bad will happen are typically the people that live in the burbs and never had their shit ripped off.