Important to know: returns are always possible, even if you don't "offer" returns. You can't get around it.

Blade measurements: if a blade is definitely, say, 21mm wide, then go ahead and say that. But do not fudge the data! Do not describe a blade's width inaccurately or optimistically. An advertisement of 25mm, for example, better darn well be 25mm when the customer measures it on their calipers, or you will likely be refunding them their cost + shipping!

The difference between 1mm can mean quite a bit of hone wear.

I purchased some Friodurs from Japan that were described as "mint" and were definitely not mint. I returned them, and would do so again at the drop of a hat. Better to be conservative in your enthusiasm for blade descriptions, and save yourself a return from an underwhelmed customer.