Did you sell much with your prices the way they were? Unless traffic was light at your sale, the market will tell you what the right price to move the fabric is. The larger question is this -- what price are you ok with? Selling our good fabric involves our emotions.
And shoplifting at a garage sale (or anywhere) is deplorable! It is awkward to confront people when there is a crowd and you are busy with the sale. But even if you aren't successful in getting them to pay, calling attention to them and letting them know that you saw it will be an embarrassment to them and may put a damper on their shoplifting.
Dayle