For selling, purple wave seems to get really good prices for their items right now. They seem to be more central us, than either coast. I used to buy some from there, but their prices lately have been too high for me. (I'm a bottom feeder, looking for a shop project, fix and sell, or fix and keep). Purchased two semi-trucks, one landoll type trailer, numerous smaller items, from their site.
I've never purchased any big iron from Ritchie Bros. I'm in the crane game, and somehow I see the same cranes floating from sale to sale, or from sale site to Machinery trader, and back. I've never dug deep enough to compare serial #'s, but there was a particular crane in texas a few years ago, that was on machinery trader, then on a ritchie sale, then back on machinery trader from one of the big national crane companies. I have however purchased a number of accessory items (spreader bars, rigging) from them.
I've purchased two cranes through Iron Planet. Both were a fair, not sky high, auction price. One, I won the bid on. The other one I was outbid, then purchased after the sale when the other buyer couldn't complete the sale. I also purchased two army surplus trucks. Both cranes I looked at in person before the sale. I don't like spending that kind of money on just some pictures and a oil sample. The army trucks were motor donor's. Also one other semi.
Probably look at purple wave the most, because their items tend to be closer to me (once-twice a month) Iron planet next. Cruise Ritchie Bros from time to time (once every two-three months). Also look at ebay from time to time (seller fees on large items are big- most have a phone # and a "available locally" part to the ad.
Really, spend the most time lately looking for items for sale on Craigslist. No buyer or seller fees. That's also where I sell any items I fix up and get rid of. Not everyone wants people coming around and looking (tire kickers), and I declare all items as is where is, but if you can wait, you'll get the most $ there. I wouldn't get the market exposure I would need to sell one of my cranes, but for a truck or trailer, not many guys from Georgia etc, are looking for a '88 freightliner dump truck out of Missouri.