All the things which in real life denote "superior craftsmanship" are not really made into mechanics, in 5E, outside of describing the weapon as "better made".
That said, you have some options:
Saves and Breakage
It's pretty rare that objects have to make saving throws in D&D in general, but sometimes stuff like acid, intense heat, or rust monsters make it a good time to make those rolls, in which case, giving advantage dice is a good call. Because this happens relatively rarely in D&D games, though (usually once every few sessions at best), it makes it hard to see superior craftsmanship as worth the money.
Fiction of wear and tear
D&D doesn't have rules for the care of weapons. Historically, you spend some time sharpening and oiling and paying attention to what's going on with your weapons after each battle. Edges wear down, get nicked, and eventually the blade degrades and cracks or breaks entirely.
D&D handwaves this, so you would basically be putting this into description - "You quickly find out this blade takes a third of the time to sharpen, and it barely catches any nicks from battle. You basically have an extra 20 minutes of time - maybe you wanna collect firewood? Sew up some clothes?"
Nice weapons indicate having money and status. Get Advantage when trying to pull rank in a military or valor context. Present yourself as higher class than someone else and so on.
Throughout most of D&D's history, a +1 to a weapon meant it was magical. That meant that pretty much everything from the crappy sword quickly hammered out to meet a quick raising of a peasant army to the finest Damascus steel weapon usually were at the same level. Or, by 3rd edition, that was an entire +1 difference.
Assuming we're going to stay within those boundaries, you can say these weapons offer a bonus a limited number of times - such as 3 times a day you can get a +1 to your rolls. This makes them clearly better than normal weapons, but not better than magical weapons. On the other hand, this is also clearly inconsistent in terms of fiction ("I'll buy 3 swords and when one runs out of bonuses, I'll switch to the next one, and so on!")
You could do something more complicated like "This weapon gives a +1 whenever you roll an odd number on attack" or "You can reroll 1's on the damage dice" or something like that as well.
Mostly what it boils down to is looking at either character abilities or magical weapon effects but making it LESS powerful as one option to including some difference.