That's not how trading works.
A merch who is asking for a price is often asking for the maximum possible amount they could make (often, this is an unrealistic expectation and they're just trying to find the right sucker)...so prices are often quite above the market's curve. Now in this case, it's more a matter of trying to barter for items of similar value, so there's no lowballing whatsoever. It's completely reasonable (and normal) to try and talk the price down to a more average value. The majority of traders are usually OK with this if the price is within reason.
Some jerks are all like: "My Way or the Highway", and those folks can go to Warframe-hell. The other day, I had a guy trying to charge 50 more plat for an item than it was worth and I told him what other people were offering for it. After negotiations broke down, I straight up said "you're just trying to rip people off, that price is outrageous" and proceeded to let him know that I just accepted one of the three other offers others had made at a more normal price...well, he didn't like that but if he hadn't been such an unreasonable dick, he still might have made a little more than market value for the sake of convenience. Now he has to try and wait for a sucker or lower his prices.
You use the word "low-balling" but you don't simply get to set the price on a whim and expect everyone to kowtow to it (such people are unsuccessful traders unless they have ultra-rare items that are highly sought after). It's a two-part agreement and both parties have some say in the matter; with the real decider being the current market price.
It's fine if one party can't accept the others' terms, but to ignore someone over simple negotiations is illogical and someone being an asshole. Screw those people, they can go to Warframe hell.
Pffft...."Low-balling". What nonsense.