To be honest I forgot to ask about their exchange policy I just assumed that if 19" feels quite ok, the 20" will do too. I was really concerned about ordering a too large bike. On some of the 19"-s (with the seat adjusted) when sitting, I could barely touch the ground. So basically when pedalling my leg was almost fully travelling down. And I also really want to get my bike already and not spend another X weeks travelling to distant bike shops on a bus in hopes to find and test a 20"+ frame