Perhaps they are sourcing them from the Eastern Europeans on E-Bay
As Joe says, those prices are too low to be believable.
Personally I wouldn't even think about buying a plasma from someone operating via a newspaper ad and a mobile phone number which is probable an untraceable pay-as-you-go number.
If you do talk to them ask them if they are official Pioneer authorised dealers and ask them how they will want to be paid.
I'm betting that the payment method will be cash or a near cash equivalent such as a debit card or a bank transfer. I'd have no qualms about paying someone like Joe that way, but anyone trading off-the-page with mobile numbers would only get my money via credit card if at all.
Mark