Personally i would rather buy a slightly cheaper car that hasnt had the belts done, then get them done by someone i trust, ie Fred @ BTM.
Rather than paying full retail for one thats just had them done by the dealer/a drunk bloke down the pub/NWP (in order of perference).
Agreed totally, at least if you have it done by someone you trust you know its done right.
That said if its recently been done by BTM/MWM/Stone etc anyway and they will confirm that, not such an issue.