Linus says:
Len, I've looked into selling my cards when they came back into circulation for standard tournaments, but it wasn't worth it. Most stores or people on craigslist just want to pick your best cards and give you 50% of their value. What do you do with the other thousands of cards?
If you had, say, 6000 cards at .05 USD a piece that's still nearly $300 worth of cards that no one wanted to buy. So they have a value of 0 USD? If I offered them for free, people would bust down my door to get them. So clearly they have some value. In the end, MtG is filled too much with people worried about money or kids that want to get everything for free. Or worse, when I let people look through them to determine if they wanted to buy, they stole my Masticore and Morphling. Kid must have had very good "Sleight of Hand" skill because I was right there watching him look at them.
Linus, sorry to hear you've had such bad experiences, especially the theft! I guess there are some pretty shitty people out there. In my experience too, MtG does bring out the greed in some people.
Otherwise, the 50% for the best cards is pretty much what I'm expecting. That is the standard rate. The game store I go to does 50% cash or 75% for store credit, so at least I could trade cards for RPG books.
As far as the 'what do you do with the thousands of other cards?' question: they are pretty much worth zero. I've tried to give them away and failed. I run a games club in my classroom where I have boxes upon boxes of cards just sitting there for people to take. Some of these were donated by other students, some were donated by game stores, most of them were donated by me. Beginning players use them to learn how to play the game, and the advanced players even use to make disposable decks. We even have a format where we 'draft' decks from the boxes - you reach into the scrambled box and pick up a handful of cards and make a deck and just go with it. Its a lot of fun! Cards like Serra Angel become game winners again.
So, I am literally giving these cards away and there is more coming in than going out! But I still have fun grabbing a bunch of cards and making some junky deck and teaching a kid how to play the game.