It really does happen to all of us - many of the rulers I have I did get when a lady left them at the rec center where my husband worked, she didn't want them anymore and the LQS wouldn't take them. But then a few rulers were bought when they were on sale at quilt shows and before I buy another one I check to see if I already have it. And I also share, when someone wants to try something, I figure if they like mine, then they can buy it. If it turns out to be more trouble than it is worth they know without the investment.
My little clover iron is one such tool - when I saw it demonstrated it looked like the best thing since the sewing machine. But it was just not the way the it was for the demonstrator.
Also, many people never make the same pattern twice, so if I have to tool and they will only need it for one quilt, why not use mine and save a few dollars?