Some of conversions I had with sellers on Gumtree:
- Can the speakers be demoed?
- No, sorry sold the amp already
- I'd be happy to bring my amp
- There's no need really. They were working before we put them into storage few years ago...
- I'd still need to hear them working though
- I don't have the wire, anymore...
My best/worst demo was with a guy who insisted that Monitor Audio MA4 (circa 1978) had very good bass. Sadly, it was because both tweeters were blown. He'd swear he can hear them working though and it was how audiophile speakers should sound.
You can never be too careful. Most of the time the biggest bargains are sadly not bargains at all.