I haven't worked full-time in a bike shop for almost 8-1/2 years, now. I don't really know if this is still the problem that it was in the late-nineties, when internet sales first became a big thing. But, we had a
problem back in those days.
More and more people began to come in the shop, trying on apparel (especially shoes), only to leave without buying anything. Eventually, we began to quiz people about what was going on, after they had spent an hour trying on every pair of shoes in the place, then leaving without a purchase.
Come to find out, they were generally trying to figure out what European shoe size was a fit, and which shoe had a comfortable feel. Then, armed with that knowledge, they would order the shoes online.
Most online bike accessory retailers, at that time, assumed that their customers were enthusiasts, and were familiar with the Euro sizing prevalent in the industry. But, most of the Weekend Warriors really didn't, and the web sites didn't have a good conversion chart in the early days.
Weekend warriors saw no problem coming to us, wasting our time, then ordering bootleg inventory off of the internet. And, much of it was bootleg. Many of the manufacturers prohibited selling their products online, in a doomed effort to propagate the Independent Bicycle Dealer business model that they were used to.
Eventually, I began to keep the boxes out of view when helping people figure out their size. Then, when they got ready to leave (without purchasing the shoes) and asked me what Euro size it was that was the equivalent to their American size, I would subtract ten from the actual number.
I wonder how many people who wore a size ten, American, went home from our store and smugly ordered their cheap internet shoes...in a size eight.