Guess I might try it later.
I just don't like the idea of scrapping weapons I farmed resources and time to build to make space for new ones.
It definitely sucks. I have a very completionist attitude when I play games like this and the thought of selling items still irritates me, but after you play the game a while you will realize how trivial it is to craft early game weapons if you ever want them back later.
The way the upgrading systems work in this game it's pointless to use weapons unless you're able to invest a catalyst and/or forma in them anyways, so hording a bunch of non-upgraded weapons accomplishes nothing in the early game other than tying up precious inventory slots. My advice to you is keep 1-2 "main" weapons per category that you like and are willing to invest catalysts and forma in and use the rest of your inventory slots to churn thru MR fodder.
As for some trading/money making tips:
Don't use the in-game chat for trading. It's a joke. Also don't use the bazaar to post items. Also a joke. That warframe market website provides the trading functionality that should be in-game.
Get used to farming and opening a LOT of void relics. Do excavation missions to farm them, since you can do 2 excavators at once and every 8 excavators you get to pull from the loot tables that drop relics. Then do quick void fissure missions like exterminate or rescue to open them. Don't do the fissures with friends or clanmates IMO. I do them with pubs because I selfishly hope that I will run into people with radiant relics and 95% of the time I'm going in with a trash relic. Even if everybody only has an "intact" relic, you should get at least a silver drop most runs and gold drops if you're lucky. Silver/gold drops almost always sell for substantial plat.
After that, just post the item on the market website (the "place order" area is at the very bottom of the main page for some reason), undercut everyone else who's "online in-game" and just sit in the clan dojo and wait for the whispers to roll in, and they should roll in quickly.
I made my very first sale via that website less than a week ago and I've probably made over 1,000 plat so far. Got a bunch of frame/weapon slots, a few color bundles because the noob colors and not having any purple were absolutely killing me, a non-noob profile glyph, and now I've got enough excess scratch that I'm seriously considering buying that ridiculous muscle suit skin for my frost prime.