Whichever offers the most value for the facility. I think the speed of disposal and the net proceeds after all fees are paid is the main driver.
Say I was a facility owner and I had a unit that owed $500 in back rent including late fees and anyother penalties legally applied according to state law and the terms of the initial contract. I wanted to recoup as much of that $500 as possible, assuming by state law any monies collected over and above that amount are returned to the tenant.
I have the option of using a free service that has few auctions listed, or another service that charges buyers a 15% fee and sellers a 10% fee and has several hundred auctions listed. Both sites claim to get alot of traffic, one site that traffic is directly to the listed auctions, the other site that traffic is to blog posts about storage auctions with a few to the auctions itself.
Say the facility was only 70% occupied and so not in a hurry to clean out the unit. They decided they could eat a cancellation fee to test out which site works better. Just in case though, they list on the free site first, ie no cancellation fee.
They list it on the free site. It gets a number of views, the majority being from anywhere in the country because there are so few auctions listed that anyone visiting the site looks at the listing out of curiosity with no intention of bidding(I know I have). The bidding ends with 4 bids for a total of $215(number made up). They cancel the auction without taking any monies and immediately relist on the other site with more auctions.
The listing gets approx. same number of views, but the vast majority are local, the auction ends with 28 bids for a total of say $475(number made up). The seller then has a 10% premium of $47.50 bringing the income from the auction to. $427.50 which is $212.50 higher then the other site.
In site 1 they are still $285 in the hole as far as what the tenant owes and probably want to attempt to collect on that still. Site 2 they are only down $72.50 and may just write that off as a loss. Theses are all hypotheticals, but it is the way I view it.
The logic is different if the facility is @ 100% capacity, they will get more money renting it out to another tenant then the hassle of collecting from the previous tenant is worth and will therefore go with whichever site can get it cleaned out fastest. Ie the site with more local traffic.
Bottom line it is the value of the service in the end result of monies collected if they are not in a hurry, no matter what the fees are. If they need to rent the unit out to someone else, it is whoever can get the unit cleaned out quickest.
Main first impression for buyers and sellers is number of auctions. Hundreds vs 6. Thats why eBay survives even with price gouging, because they are the biggest and no other auction service has as many auctions or as much traffic.
I apologize for being so long winded.