In defence of BulgarianProperties.com we recently sold our beach apartment near Varna through them, having placed it with 3 other agents. Only one other agent bothered to keep in touch (to ask if it was still for sale - after nearly 3 years); the others produced nothing.
3,000 euros is a bit expensive if your property is a cheap village house, but we were happy to pay their commission, simply because they got us a buyer!
In short: 2.5% of a non-sale proved to be zero, whereas 3k€, which was about 4.5%, released our capital and moved us forward.
They handled our sale in a most professional, fastidious, and friendly way too, which made the whole thing as pleasant as these things can be.
Incidentally the buyers were present at the various stages of the transaction once the preliminary contract had been signed, and they paid no charges to the REA, so at least in our instance we had no reason to suspect any double charging.