I made the same mistake when I bought my '75 Duster off the Mopars for sale on this site. Guy (Wannadrag) had lots of posts so I figured he was trustworthy, wrong. Here's the conversation:
https://www.forabodiesonly.com/mopar/direct-messages/75-duster.318407/#convMessage-1242312
I paid for a 360/727 car and got a 318/904 delivered. Plenty of text/email traffic until I took delivery and tried to contact him, then a ghost. Long gone from this website. Consider yourself lucky you "only" lost $300. I figure I overpaid ~$2k, based on what I was supposed to be buying. There are some great people on this site and I've bought stuff without problems. Buying stuff from people with a lot of posts isn't necessarily a safe strategy, as my example shows. Just have to be as careful as you can.