That's the best way really. I know it's an obvious thing to say, but; have a listen first, then decide whether it's worth buying.
If you want a stereo set up, then it's shame that those Wharfedale's are included, because the seller will probably like more (as in £100, rather than less), because there's an extra 2 speakers. From a buyer's point of view, they'd be paying for another pair of speakers they don't want or need. Depends on the seller, but it might be easier to get them to accept less if there were just the Technics speakers and amp.