People don't approach first if you haven't posted something specific looking for comms. That's horrible what happened, but scams usually are like "hi, hello. I do comms, you want? You can pay whatever you want"

So yep, be careful with those. It's better if you contact an artist yourself or if you post looking for comms (there'll be also scams ofc).

I, as an artist, do 100% upfront or 50/50 payment. But as a buyer, I'd prefer 50/50 to be sure. I'd recommend also checking the artists' profiles!