Now this is a modest proposal whose time has come. It's common that experimental physicists gradually (or not so gradually) accumulate some pieces of equipment over the years that are laboratory "white elephants". These items are typically acquired for some specific research project or direction, and then over the years as research goals and priorities change, they can end up sitting around gathering dust. Surely someone else somewhere could make productive use of these items. Maybe someone should set up a trading post, where we could list these things and arrange reasonable trades or purchases.
Yes, used equipment vendors exist to address these needs, but they're not not always easy to do deal with, and frequently they offer pennies on the dollar. (For example, at Rice we have an 11-year old electron microscope. It's got a problem that is likely to cost about $10K to fix, though annoyingly the microscope vendor refuses to have a reasonable return policy - if we bought the relevant part and that didn't fix the problem, they'd refuse to take it back even for a restocking fee. Two different used equipment vendors have offered around $8K for the whole SEM (!), while they both offer the same item for sale on their sites for more than $100K.) I also know that people buy and sell scientific equipment on E-bay, but that suffers from some of the same problems. The point here isn't for scientists or universities to make money on this - it's to match up scientists/engineers with equipment that they could use and that currently has the wrong home.