Class A- electrical issue?

If it is the AC side of things, the worst case I can think of is someone plugged into a 240V welder outlet thinking it was a 120V-30 amp RV outlet (unfortunately many people use the same plug compatible outlets for both). There was just a thread on one of the message boards even about an electrician that wired an outlet in a garage intended for RV use as 240V instead of 120V.

I'm guessing the seller is referring to the 12VDC stuff. Could be as simple as the battery is dead. Could also be the disconnect circuit has failed in a disconnect state or a high amp fuse between the batteries and the coach has opened. Another potential source is the AC to DC power converter has failed and the batteries are dead. Not a difficult problem to chase down if you do a bit of homework first.

It's pretty much impossible to troubleshoot with this little information. What are the appliances in question, specifically? How are they not working?

Of the three power sources in a typical RV (120V power, 12V power, and propane), usually the appliances need the following:

Stovetop -- propane
Gas oven -- propane
Microwave or microwave/convection oven -- 120V
Air conditioner -- 120V, 12V
Water heater -- 12V, propane for gas operation; 120V, and possibly 12V for AC operation
Absorption fridge -- 12V, propane for gas operation; 12V, 120V for AC operation
Residential (compressor) fridge -- 120V (often from an inverter, at least part of the time)
Furnace -- 12V, propane

Having even a slight hint of how they aren't working would be very helpful to further narrow things down -- e.g. completely dead vs. controls come on but it doesn't operate. It's entirely possible that there may be multiple problems, of course.