In case you've missed this https://scrap.tf/raffles/X7IPOO

This imgur gallery was linked in the entered message of each episode.
Here's the doc where I kept tack of every trade.

I traded for 26 days, I made 338 trades in total and my final backpack value is 372.88 ref.
This means that I made 13 trades per day on average, making around 1.11 ref per trade.

This was the first time for me not only attempting a challenge like this, but also trading for an unusual in general.

With that said, I'm no trade guru, but here's what I did/learned from this experience:
1)Check scrap.tf weapon bots and look for items like Freedom Staff, Bat Outta Hell, Ham Shank, Unique Stock Weapons (like a Construction PDA), these weapons will cost you 0.05 scrap and you will be able to earn at least 0.11 ref after selling them (I managed to sell Construction PDAs for 1.55 ref)

2)Lookout for collectors. I found a bot on backpack.tf who was buying Rocket Jumpers for 1 scrap. I sold him 106 of them, making 5.88 ref out of it. It's tiring, but sometimes it's the only way.

3)Get into painted hats trading. Some people will pay between 1 and 5 more ref for a cosmetic with a specific paint!

4)https://backpack.tf/spreadsheet
This page is responsible for 70% of my profit. I used to check the listings for every single item I could afford, let it be from people cashing out, stupid bots, or randoms, I made a lot of profit, up to around 40 ref with a single trade even.

5)Be careful with who you're trading with. I had to deal with 5-6 scammers during my challenge, all of them tried to make me login to a third party website. Trust no one!

That should be it, the more you own, the easier it gets to make profit, it took me 250 trades to get my first key, and I managed to make 6 more with the next 88 trades!