Selling can be extremely irritating. You generally operate on very small profit margins. There's no shame in only making a scrap per item. I've found that one of the most profitable ways to sell low- tier items is to go into public servers, and say something like "Hey, anybody want a festive rocket launcher? 1 refined and 1 reclaimed".
I bought that rocket launcher for one refined. The one reclaimed was pure profit. It was only worth one refined, but the beautiful thing about public servers is that nobody has any idea at all how to trade. You can sell items for whatever price you want if you're a good enough salesman. Sometimes, though, you may need some outside stimulus to sell an item.
Tip #2: Have a friend glorify your product.
I spent about two days trying to sell that festive rocket launcher with no luck. Then I was playing with my friend, casually chatting about it as usual, chatting my message above. Then out of the blue, my friend publicly chats: "Dude why are you selling that for so low? You could easily get double that. I'd buy it if I didn't already have one". I immediately got a trade request. It sold.
Try to sell your products for more than their worth, and most importantly, more than you bought them for. If told about the spreadsheet value, save face by pretending not to know about the spreadsheet. It may take time, but some 10 year old who's daddy just bought him the game and gave him some steam wallet cash will be more than willing to pay double spreadsheet price for your Teddy Roosebelt. Don't think of it as taking advantage of people's ignorance. Shame on them for not researching the product before buying and selling.
Chat to all players that you "Have an extra Armored Authority (Soldier Helmet), selling it for 1 refined 2 reclaimed, 2 scrap". That's my current offer. If I sell it, which I will, I'll make a .55 profit. It's a nice hat, my soldier wears one, but I bought it for what it was worth. When selling hats, make them sound awesome, and sell them for a lot. And if you're selling an uncraftable hat, don't tell people that it reduces the value. That will just bring down your profits.
Lastly, be observant. If you see a player using a Southern Hospitality, and remember that you have one on hand, offer it to him for "the low price of 2 reclaimed and 2 scrap" (it's worth 2 reclaimed). People not familiar with trading think that strange weapons are extremely rare. Capitalize on this. If you see a heavy walking around with a Gibus, offer to sell him your Magnificent Mongolian for 1 refined, 2 reclaimed (1 rec profit). Slowly but surely, you can make tremendous profits.