What are you thinking of buying mate and who from?
Post count is a good indication, tho not perfect...take me for example...I have the 10th highest post count on here...but, there aren't very many people on here who have met me in person.
However...that didnt stop Paintball budgie, from having a marker sent to me, by the guy who was selling it, for me to put some bits on..and have it for like 2 months, coz PB went on holiday!!
Likewise...he also sent a dynasty shocker(£600), to a friend of mine, who doesnt even use the forums, for him to see if he liked it, before he paid for it!!
Thats the sort of trusting place this is.
If you wanted a third party, I would do it mate, but not really neccessary if your buying from one of the regulars in here.
Get a Paypal account if you can, as that can make things easier.
Still, caution is seldom foolish.