There are some things you should really see/inspect/measure before you buy, but in the age of item reviews and free return shipping, laziness often dictates that we just take a best guess and see how things play out.
Recently I ordered a wetsuit even though I know nothing about wetsuits. Return shipping was £10 so I felt like the stakes were pretty high, and yet I couldn't bring myself to go to a sports shop and either just check em out in the showroom or just buy one there. Both options would have been a great way to guarantee success. Instead I read a sizing guide, ignored the minority of commenters who said my selection ran small in favour of the majority that urged me to size down, searched my feelings and clicked "confirm order." And you know what? That wetsuit fits like a frickin glove.
Of course I had to return the bathmat that was too big for my bathroom, the replacement mug that didn't actually match my other mugs, and the piece that was supposed to hold my bike seat in place, but boy does that wetsuit fit. Give me your best guess below.