It happens a lot in all areas not just quilting. If I want something specific I usually check it out on-line for several reasons.
1.) what does it cost and do I still want it
2.) where to get it locally or is it better to have it shipped to me
3.) if I am impulse buying, then I try to avoid looking on-line because I know that it will be cheaper somewhere else.
When it comes to buying a roll of batting, I prefer to buy it on-line because it is cheaper and it is delivered. (Stores rarely have anyone available to help you out to your car here.)