I've been looking for 3 used DVDs so I check the listings fairly often. I don't know if it's just my imagination, bit it seems that used DVDs along with other magic apparatus seems to have taken a nose dive pricewise. I'm also noticing a lot fewer used DVDs listed and a lot more magic for sale. Sign of the times?

I think magicians have come to the conclusion that DVDs just don't hold their value the way a quality book or trick will. Many now simply prefer downloads to physical DVDs. I still prefer the DVD myself. DVD's also seem to go on sale when new more often than books which naturally leads to lower selling prices on used DVDs. If you are going to spend your money on magic and you consider the resale market in case the purchase doesn't please you, then I can understand why DVDs might be declining in popularity.

The fact that downloads and ebooks have essentially no resale value probably keeps many magicians away from them, but the digital revolution marches on none-the-less.

If you subscribe to the "law of supply and demand," a larger supply leads to less demand and lower prices. In the used magic market, the ease of selling used material in this era greatly increases the supply. It is unlikely magic's appeal to the general population has increased our ranks to the same extent so that would lead to lower prices.

Of course it is now so easy to produce digital magic that the average quality of the products on the market could be lower than before leading to a general reluctance to pay the higher prices seen in the old days of video magic.

Buying magic with resale value in mind? Hard to digest for me, if true.

I believe that it depends what you are buying. If it's a good set of cups for example, the resale value would be a factor for me. Spend $300 bucks, and if I take care of them, and decide to sell them after a year or so,, it will cost me maybe $50. If I love them, I'll keep them. Not great, but not bad.
.I felt the same way about DVDs. Buy used, don't like it, sell it and lose $5 or so. It's kind of like renting. Can't do that with the downloads. The downloads are so much less expensive, that if one is available.they're almost half the cost of a disc.The problem is that they aren't always available as a download. (Right now, I'm looking for Kozmo's Tales From the Street. Not available as a download yet. The way things have been going for me, they'll probably announce a download right after I buy the DVD.)

You are misrepresenting the law of supply and demand.

Let me guess as to what you mean since you didn't expand on your thought. A larger supply does not actually move demand one or the other - it only affects the ease of fulfilling whatever demand exists. I actually paused myself when writing those words. My statement used the leap of logic that a larger supply would truly lead to more of the demand becoming fulfilled and therefore less demand (unfulfilled demand) if there was not such a large supply. Truly owners and hungry buyers could all sit on their hands and do nothing, but I think things would actually move along according to my thinking.

The way I understand the law of S&d is that iy effects the price of goods sold. If there is a glut of oil, gas prices go down. If demand causes a shortage of oil, the price goes up. Cost of replacement also has an effect on prices.
As long as Sherwood cups are in short supply, those who want them will have to pay a premium price to buy them. If the price wrises significantly while you own them, it is likely that you can sell them for more than you paid for them.