There were a few occasions where the manager (owner's son) of the shop I worked for in the mid 90's would ask a customer to leave for "pestering employees" because they'd walk around the store quoting Performance/Nashbar/Excel/Colorado Cyclist prices for items they saw. It's a judgement call, but some customers are bound to do more harm than good, and it's sometimes (albeit rare) better to just get them out of earshot of other customers.