Its either:
Trust them to send it once you've sent them a cheque.
Meet them and pay and handover goods face to face.
Or use an escrow service - this means you pay money to a 3rd party, they instruct the seller to ship the goods... you get the parcel and check it over, if its ok you tell the 3rd party and they pay the other guy - transaction costs are a couple of quid.
I dont know what UK based escrow companies there are, but thats the general idea.
if you do have to send a cheque off then make sure you get as much info about them as possible, full name, address, etc etc - and if they do pay the cheque into your account and dont sell the goods - you have details on them as your bank will have records of what account it was paid into.
Jamie
Fiat Bravo 2001.
Nakamichi CD40z/Stock HU
Directed 1500 Dual Input EQ
Stinger Dream Series Interconnects.
Rockford Fos Punch 100z2 Per Door.
Rockford Fosgate 5.25 Comps.
4 Directed Dei1100d's Cerwin Vega Stroker 18D2.
Predicted SPL - 160+Db