I've bought lockers from their owners twice. The benefit is you generally get to look much closer, look in boxes etc. On the first one it was a family with grandma's stuff. They had tried to sell out of the unit, garage sale style a couple times but it was packed really tight and they had only made back a couple feet. I think it was a 10x15. Tons of boxes all marked with tempting things. Paid $900. Got past the packed to the ceiling boxes to find tons of broken furniture. After costs, made maybe $600 profit. Lots of work, had to really make an effort to make a profit. Not a very good experience. On the second one, about the same size, paid $400. At initial viewing the owner kept pointing out items he was keeping. There was a $600 coffee maker in sight. He kept saying how valuable it was. Told him to get his "I'm keeping that" stuff out before we would pay. Came back to find coffee maker gone. Told him we wanted it or deal's off. He brought it back. Paid him and started to clean out locker. He stayed and watched and kissed all his "beautiful things" goodbye. Seriously! He called us several times over the next few weeks to ask if we had found certain things he wanted to have back. A chef knife, a drawing, a gold and ruby ring. Found the chef knife, nice but had a nick in the blade (gave it back to him). Didn't find the drawing, found the ring but had already sold it before he asked about so we told him we didn't find it. We ended up getting a little over $500 for the coffee maker on EBAY. Overall, made $1700 profit on that one. Good money, awkward experience.
My advice about buying from owners...if they say they have been selling stuff you can be sure they sold the good stuff, and if they seem attached to their stuff make sure they leave before you start emptying the locker.