How to trade CSGO Skins? Is it still profitable?

[Monetizing]

Since I'm only playing CS:GO casually (total hour about 120+ only), I don't really know much about the skins market.
Just wondering if someone can tell me how these people buying skins constantly make money?

And why most people willing to sell at 60~70% when they can get better price via websites like OPSkins?

I do understand buy low and sell high, but isn't skins have low liquidity(hard to convert into cash), and when the price drop you lose money?

[Gaar]

For the most part trading up is impossible because people will do trades that make $0.20 even if its an ugly skin. And when everyone does that it's really hard to make any money.

[HenHon]

If they sell it on steam they can't cashout ther money.
If they sell it on opskins, g2a, bitkisn etc... They will get the 70% of the skins "market" price (steam market) so they can cash out that money. They can't sell it on 100% beacuse if that would happen everybody would be buying skins off steam market so it would have no point.