I wouldn't do this unless I had bikes I truly didn't care about. A careless renter locks up poorly or not at all? Your bike is gone. They crash? Your bike is messed up and they're probably going to find some way to blame you. Jerks decide to take your road bike off some BMX jumps? Forget it.
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1964 JRJ (Bob Jackson), 1973 Wes Mason, 1974 Raleigh Gran Sport, 1986 Schwinn High Sierra, 2000ish Colian (Colin Laing), 2011 Dick Chafe, 2013 Velo Orange Pass Hunter