I am an analyst for PriceCharting, so I have a bit of experience here. The cataloguing feature is fantastic, and Ive used it for years.
The values they assign: not what you think. The values listed on PriceCharting are *not* what you should expect to receive as a seller for selling any particular title or system. Moreover, they are also *not* what you should expect to pay as a buyer. It is a tool to detect valuation trends ONLY. There are *many* dynamics that skew and distort valuations, and there are currently no remedies to mitigate. For example:
1. Loose cart values do not factor in lot prices. When buying games in a lot, you can expect to buy/sell at a mere fraction of the aggregate values listed. If you are selling a 20-game lot, and each of those games are valued at $10 each, you will never NEVER get $200 for that lot. Your item will remain listed for years without a single bidder.
2. GIGO ... PriceCharting is merely a web scraper that pulls transactions from eBay. Values do not factor in erroneously listed items sold, and their algorithm yield an extraordinarily low accuracy rate with regard to sale type (loose, CIB, NIB, manual only, box only). There are NIB entries where the actual sale was a CIB, and there are loose cart entries where the actual sale involved box only. That's where us analysts come in a line-by-line report bad data. There only so much a handful (hundreds? thousands?) of analysts can report and the dataheads can reconcile when the site adds thousands of entries per day.
3. What they *don't* consider. Let's say there are 100 people who want to sell a loose Atari 2600 Pac-Man cart. They go to PriceCharting and see the value listed at $5.00. Now you have 100 sellers who actually think they'll get $5 for their games. All 100 list their item at $5 for 30 days. One lucky seller within that timeframe got some ignorant sucker to engage in a $5 sale, and the other 99 predictably had their listing expire. If you are selling 100 of something at $X and only 1 person buys that thing at that price within 30 days, then that thing is worth much less than $X, however, that one sale is scraped by PriceCharting, self-validating thir own bloated price of $5.
4. Shipping. I won't even get into the fact that PriceCharting values do not factor in shipping, so even that $5 sale had an associated $2-$3 shipping cost attached to it.
5. Quality. The value for a mint condition, just-pulled-out-of-a-NIB loose cart, and a nonworking, busted up cart with no label is the exact same.
6. Under/overvaluation. Although nealy all items are overvalued at PriceCharting, there are some that are clearly undervalued and do not take into consideration rarity of an item. There was at least a year that I can remember where I couldn't find a Cosmic Commuter cart to save my live. One was finally listed and I was lucky enough to bid $10 on it and win and even luckier that the seller mistitled the listing ("Atari game for sale"), which would certainly not catch the eye of most of the collecting community. I would have easily paid triple that. That $10 sale skewed the PriceCharting value downward. This rarely happens, but it does indeed happen.
In conclusion, I would take PriceCharting prices with a grain of salt, and I would advise not to have lofty expectations as a seller, and not to get hosed by inflated prices as a buyer.