Type
The machines themselves, from Atari's wood-grain 2600 to the gray PlayStation. A used console has usually been in a closet or an attic for decades, so the checks are the same ones every time. Does it power on and play a game from start to finish? Which revision is it, since the same name can hide very different boards? What does it put out, and what will your TV take? Is the power supply the right one, and are the controllers original? Look at the screws too. Stripped or mismatched screws mean someone has been inside, which is fine for a recap or a mod the listing names and a worry when it doesn't say.
11 models we cover.
Atari 2600
Console$180–$420 typical ask
56 on eBay
Atari 2600
Console$70–$150 typical ask
125 on eBay

NES
Console$95–$160 typical ask
157 on eBay
NES
Console$190–$320 typical ask
71 on eBay

Sega Genesis
Console$75–$150 typical ask
76 on eBay
Sega Genesis
Console$55–$110 typical ask
118 on eBay
SNES
Console$120–$210 typical ask
196 on eBay
SNES
Console$140–$260 typical ask
68 on eBay

PlayStation
Console$80–$160 typical ask
63 on eBay
PlayStation
Console$65–$110 typical ask
179 on eBay

Nintendo 64
Console$85–$130 typical ask
170 on eBay