I've been reluctant to even have my OWN garage sale near my facility, let alone host one for tenants. I think that many might get the wrong idea as they arrived on site and saw me selling items that looked very much like the ones they are storing....
Although I have room in the street on weekends to allow many tables and parking for a yard sale, I haven't wanted to give people the means to get rid of their stuff and downsize or move out, in addition to how I think it looks to prospective tenants.
I too had a tenant that used 2 very large units to store items that he sold at the flea market on weekends, he was with me for many years. At some point he stopped paying his bill and never came back. We opened 2 units absolutely filled to the 10.5' ceiling with junk that would not sell even at the flea market. Slowly the junk overtook the saleable stuff, to the point the he just walked away and left it all for us to deal with.

Now I'm very suspect of flea market types.