Because they relate the exploits of others to NPCs, of course. Our parties usually have a bard, or a paladin, or both, very communicative folks. In our Odyssey of the Dragonlords, we have a ship full of NPCs including multiple bards, and the goddess of Music to do our PR, as Fame and Prestige are tracked stats.
We've had - and have still - a few characters who are really big on the self-promotion piece. The rest of us either ignore them or laugh at them, most of the time.
I rearranged the order of some of the quoted bits below to put like things together.
Except that the principle of 5e (you might like it or not) is that there is simply no market for items, not enough items on the market, not enough buyers, not enough communication means and, even more importantly, not enough trust that it will not be stolen at one point or another.
I guess I should ask: is it your general assumption that the PCs are the only active adventurers in the setting? That can make a big difference here; and I always assume there's other adventurers out there willing to do, or try doing, what the PCs don't or won't or can't. (and if there's no other adventurers out there, where do replacement PCs or henches come from?)
"I'm sorry, I won't accept that estimate, the value from three people who are little bit more than brigands does not mean anything to adventurers like us".
The designers and I don't agree. What gives you the impression that showing a sword to a few mercenaries will give you an estimate of the value of such specific items to high level adventurers ? It's just as dumb.
Terminology mix-up perhaps. When I say a mercenaries' hangout I'm referring to the warrior equivalent of a Thieves' or Wizards' guild or Clerics' temple - i.e. the sort of place where other adventuring types can and often will be found. Put another way, the same sort of places you'd go if your party was looking to recruit a replacement Fighter, or hire a sneaky type as a hench.
With this, showing the sword around these sort of places
will put it in front of other adventurers who will have at least a vague idea of what such a sword would be worth to them and who thus might make an offer for it.
We have been running 5e for maybe 20 campaigns since we started, not one with monetary value for items, although there was trading, and it went absolutely fine.
Another trivially easy way to determine an item's in-setting value is to take it to an artificer and ask "If I wanted another one just like this, how much would it cost to have you make it for me?" Whatever the answer is, boom, there's your item's base value.
And at the same time, none of our DMs are that one-sided and stupid, so we don't have that problem either.
That right there tells me your DMs aren't being truly neutral arbiters when running the game, which raises a very large red flag.
That is a house rule, good for you if it works.
Only partly; 1e had training by RAW, we've just modified how it works.
Well, it's not the case at our tables, and we think our collective and collaborative play is much better for it (once more, not preventing discussions and dissenssions, but focussing on heroic things and plans).
I'd love to try playing a character at your table*. Not sure how long I'd last at it and I'd probably upset a few apple carts along the way, but it's be all entertainment all the time as long as it lasted.
* - though despite being Canadian I speak virtually no French, and I seem to recall you're in France...?