Lord_Britania: The keywords are luck and patience. In fact the ressources don't really matters, except if what your seek is something really collector or huge. Exemple Steel Battalion on X Box with his marvelous controller.
Perhaps someone will sell something too much, wait, see another seller, trade, etc... Last time i checked FF7 non platinum here was 70/80 euros, i paid mine 20 euros on ebay. CDs quite brand new with its booklet.
And about chance i get FF8 non platinum for 3 euros, because the mother's seller didn't know about it and the game was hidden with music albums ^^'
A big problem with the retro market is that many games are massively overvalued, especially here in Germany. You have a lot of commercial traders on the likes of eBay and Amazon demanding ridiculous amounts for games that are supposedly rare but are plainly nothing of the sort. Mario and Zelda games are a key culprit in this regard. We also have the same problem with commercial fleamarket game traders who demand ridiculous amounts for their games, although I've solved that by now only going to fleamarkets in smaller towns.
You get a lot of idiots charging 20-25 euros for Super Smash Bros. for the GameCube for example - no box, no manual, just the disc. I have to wonder sometimes if these people have completely lost the plot.
As you say, it comes down to patience and luck. At fleamarkets, you'll always get better prices from private sellers who are just clearing out their basement or getting rid of their old games. Charity shops and thrift stores are often good sources - I've picked up some classics from charity shops in the UK.