I've not had much experience with compacts, so don't know of their inherent issues. I'd say don't pay much if you buy online, but being "untested" isn't necessarily a scam.
I interpret "untested" differently depending on what other items the ebay seller has. If they specialize in camera equipment I'd expect at least a cursory test (it can be daunting to test everything thoroughly) (I also expect good photos of the items from sellers of cameras). If they have the odd piece of photographic equipment or as stated above inherited something, I don’t' find it as problematic. Even before digital there were many people who had no clue on these things.
Either way, one must be careful, and I generally expect "untested" cameras have a lower price or I'm not interested.
As an example, one seller said he couldn't test a Ricoh XR-7 because the button on the bottom wouldn't turn it on. You know, the button that releases the film for rewinding. Some sellers don’t' know that some older cameras need batteries, or that others don't. Again, if they sell photographic equipment I'd expect them to invest in a few batteries to test. Also, they are already on the internet, so it's not a great inconvenience for them to search for information before listing.
I have a box of ~18 Ricoh XR-7/Sears KS-2 cameras I bought cheaply (and individually) for parts, so I did not care how well they worked. Half were "untested" and all were sold "for parts." Only one was actually broken. The rest just had dead batteries and degraded light-seals, or the sellers didn't know enough about cameras. One was in excellent shape and I gave it to my best friend.
Back to compacts - do you need all the bells and whistles? Do you need any? Some very basic fixed-focus compacts with a thumb-wheel advance can be fairly robust. They may not have many features, like more than one shutter speed or aperture, but they have fewer parts to go bad and often the only electronics are for a built-in flash.