I've ben fortunate enough that several people have let me test props before purchase. One set I knew right away that I wanted them and paid the guy, another set I wasn't sure about but the guy wanted them back quickly so they went back(In hindsight I wish I had bought them), the third took me a second day out on the water to determine how they performed and then sent them back. In all 3 cases I was in contact with the sellers at least twice a week, confirm their arrival, how tests went, and how/when they would be shipped back.
These are just the shipped props, local guys have let me test a number of props too. All 3 of the above were in my possession no more than 2 weeks.