Buying online is not the same as going to a shop/store hunting through the stock for the item that seems just right. You can see them holding them up to the light, touch them feel the weave and the weight, and then to actually try them on.
The changing rooms were always dodgy, you couldn't trust the locks but you could pose in the mirror.
Sometimes you'd see boys with their mum's trying on speedos or shorts then coming out of the changing room to pose. Buying sportswear can be a family affair.
Trying on swim briefs should have that wow effect when you look in the mirror, perhaps your first swim briefs were black or navy but there is the dare and excitement of trying on something more colourful or brightly patterned or more skimpy. When you try them on if you don't go wow, they're the wrong ones.
Having made your choice with the swim briefs in one hand and cash in the other (never use a credit card to buy anything personal in a shop) and hope that the assistant at the till doesn't notice your "excitement" as you hand over both product and cash.
When you visited another town or even another country there were always sports shops to explore for something a little different.