This would only work for high value items, or 'semi-fungible' goods with an easy to determine resale value (e.g. books, media, smartphones). For the latter it probably wouldn't work either. You already have things like Eco-ATM and the BookScouter app that let you quickly and easily liquidate an old phone or a stack of books, etc. It's more work than donating (you have to sort through the books, generate an invoice, etc.) but you get some cash. If donating were the same process, many people would probably opt for the cash.

I've known people who made six figures driving around to thrift stores, buying up any books worth >$10 and shipping them straight to an Amazon warehouse. I do believe I've also heard of some Goodwills scanning book donations and sorting out the valuable ones themselves for resale elsewhere.

Someone mentioned "stuff arbitrage" below and I think this is really the value goodwill, et. al provides. Sorting and classifying donations provides a lot of overhead that doesn't scale well for things like clothing. In the past when I was broke and unemployed I used to go to Goodwill and buy a bunch of low-middle end designer clothes (Levis, Ralph Lauren, cashmere sweaters, etc.) for $3-5 a pop, and sell them on ebay for $20-50. The margins aren't bad, but it's a labor intensive endeavor. Between finding the right items, inspecting for defects, cleaning, measuring, photographing, creating an ebay listing, shipping and handling, etc. I made maybe minimum wage. Called it quits after ebay raised their fees for the umpteenth time.

If I'm understanding your idea correctly it would make donating more complicated, meaning less donations. Additionally, if you have things at a thrift store priced at "market value" you eliminate a.) the social benefit of making low cost used items available to the community (think a homeless guy buying a suit for a job interview for $5) b.) the fun of finding that hidden gem, which is the real reason most people shop there to begin with.

For things like art, high-end furniture, musical instruments, it might make sense though.

If someone can solve the huge drop in people who donate if they have to put in any effort it would be amazing.

Facebook has done it essentially already with their donations

Goodwill has a natural time delay that gives a chance for things to die off.