Agree 100% with you.
I try to test the stuff I get given, but if it's going to take a $20 battery to do so, I admit I'll think twice. I'm not trying to rip anyone off; if I haven't tested it, I'll indicate as such - entirely the buyer's call as to whether they want to take a chance.
On a different note, even testing one won't guarantee it works. I sold a Mju that I inherited from my uncle - it worked perfectly and the shots were amazing. Unfortunately, it had a battery drain - after a few days, the battery would be dead even when the cover was closed. I didn't realise and sold it in good faith. The buyer got in contact a week later (after testing a second battery) and I refunded the price in full.
Sure, there might be some out there who want to make a quick buck on a faulty camera, but deciding that everyone who doesn't test a camera is a such a seller, is rather narrow-minded IMHO. Feedback is a good guide - but even a 100% seller can attempt to renege on a faulty product and you have to stand firm and fight to get a refund. (Don't ask me how I know . . . )
Personally, if it were an "untested" camera, I'd do my sums and work out if it's worth the asking price. Then I'll either get a working camera or take the hit on it being useless. Ball's in my court, I just have to figure out how I'm going to play it.
Naturally, as always, YMMV