You are so right. I have never gotten a bad deal on eBay but, I don't buy all that much on there. I am currently waiting on another G4 iMac 1.25 Ghz from usedmac.com. I have never bought from them but, hoping it's going to be good. I called about buying it and asked if they put new displays in them because many are real dim. The guy said you can't get a new display for it (17 inch G4 iMac). I don't think that's true.
Unfortunately, it is more or less true. iMac / PowerBook displays of that era use CCFL backlight and those CCFL tubes fade away with time. They will be not as bright as when they were new and colors also will shift to yelow-ish end. Blue phosphor. is the first that burns out. (Been there, done that, tested/tried to calibrate well over 20 displays of that kind and age).
The solution to this problem is either
(a) using donor display panel from iMac or PowerBook, if it is still in good condition;
(b) finding NOS display panel of the same kind (expensive);
(c) finding replacement panel produced more or less recently by a 3rd party (expensive);
(d) replacing CCFL tubes in original display panel. These can be sourced from far east. (DIY job).
All these also are very labour intensive. Nobody will do it for a tenner. If you have the skills, go for (d). If not, leave it as it is.