It's my personal opinion that any collector, (of any hobby, really,) should learn the delicate art of appraisal. There's really never going to be an ultimate authority on what anything is worth, since so many economies are at play. Fluctuating figures on a day-to-day basis mean that what you'd ultimately be willing to pay for a game today could very well change tomorrow or next week.
My advice has always been to just use Price Charts as a starting point, (or a very loose summary of the current market if pressed for time,) and go ahead and do the research yourself. One's collection really should be quality over quantity anyways, so plan a purchase ahead of time and grab the current numbers yourself. Don't be afraid to set limits as well!
An example: For years, I've been in the hunt for a CIB copy of Castlevania Legends for Gameboy. Even though it's the only Castlevania game I don't own a complete copy of, I still can't bring myself to pay more than $100 for a subpar Castlevania game, regardless of rarity. So, I check PriceCharts to see what they value the game at, (as most vendors and collectors use this as the only resource for game values - I now know where they are getting their prices from.) Then, I'll hit up eBay and compare all the CIB prices of completed listings, making note of the highest and lowest 'sold at' prices, while also taking note of the mean of the remaining 'sold at' prices, (mean = total ending costs of all auctions added up and divided by the # of auctions.) I now know what the game has recently been fetching at auction in the wild. Next, I'll browse amazon.com and compare prices, (9/10 times, the values are the same withing $5 or so..) So, for a grand total of about 10 - 15 minutes of research work, I now know what I should expect to pay for a CIB copy of Castlevania Legends. And, as per my personal spending limits, I'll refuse to pay more than 85-90% of the going price, (unless it's a full on trade, in which case I try to go 100% for 100% of the value of the trade items.)
Anyways, this is just my recommendations for anyone getting into the hobby of game collecting, or anyone else interested in a tried and true method of video game appraisal. For newer games, Gamestop.com is an invaluable resource as well for checking prices on current-gen games, since it's hardly easier than just walking to your nearest Gamestop and picking up your game that day, free of shipping costs.
Also, iPod/Touch/Phone users can download an app called Video Game Trader Price Guide (VGT Price Guide) from the app store. It's an aggregate of PriceCharts and for the most part is pretty reliable. I use it since mainly due to it's convenience and portability - it's handy as hell for yard sales and flea markets. However, again, it should just be used as a jumping off point for your research, and never as a definitive authority.
Do your own research and save some money. Learning to haggle effectively isn't a bad idea either..
