Don't blame you as far as ebay goes. Here's a few things to look for in a used laptop:
Look the screen over thoroughly for missing pixels and blank spots around the edges. Listen to the hard drive closely. It should be almost inaudible , same with cd/dvd drives. Check the power input jack. This is a common point of faiure. Do a cold reboot of the machine to ensure cmos is working properly .Check all keys, mouse buttons etc. for proper function. Check the lid hinges and associated hardware. This is another common problem with laptops. If it is currently running windows, you can get memory/system diagnostic programs on the web to test with. Finally make sure modems/pcmcia / usb devices all work properly. Good luck