OP- express your concern to the Buyer (thats fair)- ask them if they could email you from their work email address. Still not guaranteed safe but at least you have some sort of stability/steer. If they say they dont have one then to be honest, if its alot of money I'd only buy/collect. I only get high-value posted if I've satisfied all my concerns.
I bet alot of ripped off people keep quiet. i,e 'missing in post' and other areas that could go either way. STW classifieds arent saintly or a friendly-club. Sorry, I dont believe that.
If not totally sure- dont take a punt with your money. Its not worth the risk.
Hey mieszko- the watch you sold me is SPOT ON. Its stunning. The face size actually suits my wrist. The strap is on the edge of being too small though (darn my peasant-wide wrists!) 😀