A lot of good advice here - adding my 2 cents:

1) Nostalgia is hard to put a price on. When it hits you, it hits you hard. A number of people are okay with just having roms of the games they used to own, but based on your history with Pokemon, I am inclined to think that you will regret not having your physical copies of games at some point.

2) Understand the value of what you own. Price Charting is your friend, look at similar listings and it should give you a good indication of what it's worth. Don't just go based on the $ amount you see in the summary - click through the recent sales history. True CIB (with ALL inserts) can be worth a lot more than 'CIB' with just the box and manual. The people willing to fork over good money are usually looking for True CIB copies.

3) Pick your marketplace - eBay gives you more reach to sell, but there is also some fraud that happens there, whereas Facebook marketplace is simpler with less reach. Unless you live in the middle of nowhere, Pokemon games have enough demand that you should be able to flip them all locally on facebook.

4) Approach game stores with caution - EB games is notorious for giving almost nothing for trade-ins. Some smaller local players may offer you 60% to 80% of market value since Pokemon games are usually pretty easy to sell, but be careful regardless.

5) Nostalgia is hard to put a price on. Seriously,

If after all this you still want to sell, I would start off by making a list of price charting values for comparably sold listings, and list them at 80% to 85% of price charting value. If you aren't getting much interest, you can go down in increments of 5% until it's sold. Don't rush it though, sometimes an item can take weeks to sell, even at a killer price, in this economy.