If it's a CB500 twin, it's worth about a dollar a square foot, they weren't one of Honda's better efforts. They should have been, but Honda turned a gem (CB450) into a dog. They vibrated so much, riders were known to involuntarily wet themselves..........
"Sight unseen" is a dangerous term. I recently sold a Suzuki GS750 on Ebay to a bloke from New Zealand. Really nice guy who knew I was into GS1000's, so he contacted me and said he'd found a genuine "one owner" GS1000E with some Yoshimura parts installed for only 300 bucks, did I want it?
I said yeah, I'll take it "sight unseen"............... Well to say I was disappointed when I first clapped eyes on it is an understatement. First of all, he thought that 300 bucks wasn't enough, so he gave the woman who owned it 450, she must have been 'rapt. It looked like it'd been pulled out of a drain full of salt water, it'd been bashed, crashed, then bashed some more.
My Kiwi mate didn't realize that the tank had been resprayed, (no decals) and the white stuff under the missing paint was old bondo. The PO had cut bits off the frame for the Yoshimura race pipe (now just a rusted-thru memory of it's former glory) to fit, the brake calipers, engine cases, fork lowers etc were covered in a thick layer of oxidation, and everything else was either rusty or crudded up with chain grease and mud.
What did I do? Yeah, I bought it anyway............. I "gingerly" pulled the plugs, and as the bike had sat since leaded fuel was still available, they were still a nice "tan" color. I pulled the carbs, cleaned 'em, put some fresh fuel in it and it fired right up on 4 cylinders. I took the cam cover off and the cams look stock, but I'm told it's been treated to a 1085cc big bore kit.
It feels nice and strong, and I've just repainted a spare frame so I'll have it all together next weekend as a complete bike again, but I learned an important lesson about agreeing to buy something "sight unseen"..............