I have been in business for 6 years and have only had 2 returns that I can remember. In one case it was a gift of coffee from someone else but they needed a different grind. I happily shipped them out the correct grind, no charge. The other case was with a wholesale customer and I am not getting into that one. They are still a customer.
Taking returns is not going to break your bank unless you are selling crap. I think people just want to know that they have the option of returning it. It gives the consumer peace of mind with the purchase. If they do return it you know they are really not satisfied with the purchase.
I got a Tifanny's pen years ago as a present. About 4 years later the two ends no longer stayed together so I went by the store and asked if there was anything that could be done to fix it. The salesman took it apart and put it back together several times and then handed me a "new" pen, no charge.
It is that type of customer service that people will talk about and tell their friends about which is part of the reason they are so successful.
I lost the pen a few years later so had to go back and buy a new one

which I did because I loved that pen and the way the company stood behind it.
I think selling on the internet the best thing that you can do is give the customer all the information needed up front so when they get the product there are no suprises. ie if you are selling clothes and you just put in your information that it is a size 6, ask a woman what size 6 means and they will probably tell you it means nothing. Put the actual measurements of the clothes and then the customer can make an informed choice as to the proper size for them and cut down on your returns. There is a reason clothing stores have change rooms.
Peter