If it is recently fully serviced it is worth much more then one that has just been run hard and put away. Say the chain bar and sprocket look 75% like new+ ,it starts and runs good, I would check the air filter and see if its clean and in good shape,say it is, say the general cosmetic condition is good which means no cracks or breaks and few scratches and plasic appears to have good color . I would go $250 to $300 if I needed that saw, as a matter of fact I sold my best o26 pro for $275 about 6 months ago to a professional excavator. This saw was ready to go to work. If the saw looks like it needs some service you can easily end up putting a hundred dollars much more or less into it depending. Bar,chain and sprocket ;$50 to $75,AV mounts are close to $10 each and there is 4 of them to give you an idea how repairs add up and don't forget labor cost.
I hit a fair amount of auctions myself and I like to either go the day before or just plenty early so I can start and look engines over thoroughly. Also the day before you can often talk to some body that knows the items history.