I had a chat with a person in support. I will localize my problems with the bot, other then pulverize my confusion.
1. It does to offer a full stock of cards it has.
100%, this is a fact. I could count the cards manually, but I don't need to. It becomes obvious if you look at card sets, in the row "Cards in Stock", there you can see that the bot for example has 23 cards available, 5 of them forming a single full set of cards it has. If I would to buy a set then 18 of the cards remaining would not appear in a catalog to be bought manually, they will just vanish, which leads to a problem namba too.
2. Some cards are either in sets or in catalog, but never in both.
Example: there is a possibility that you can buy a full foil CS:GO cards set from a bot's manual catalog, just a full sets all at once in single trade. BUT! It will never appear in "Sets" tab. Never have I ever seen a full foil CS:GO set for sale there. Just like I've never seen a single Skullgirls foil in a catalog for example, even though I've bought a complete set from "Sets" not so long ago. So there we have it, a problem number 3.
3. Cards are hardcoded to not be shown.
I am certain of it. I am 100% sure that some cards are coded to only be sold in sets, and some in catalog. And it is kind of understandable, but it leads to card not being shown. Just before it stopped working right now it showed that it has 42 sets in stock, while I could only see and buy only 3. Cards in catalog are the same thing. Support member made a point that steam's API also has a big part in not showing bot's inventory, and yes, API's an old stinky pile of broken bad garbage. But the bot knows that it has 18 more cards, it sees them, and is still not showing them. And for all the cards that it does not see because of API:
4. There is only so much 1 bot can do with 500k cards inventory.
510000 items in bot's inventory actually probably lead to a good portion of them not getting featured in it's stock because it simply can not load them all at once. I am not 100% sure, but I am decently confident that a long time ago there were actually 2 different bots doing all the work, compared to 1 struggling right now. I do not think API can or will ever be fixed, so to me the only solution to a problem is to just host a second one. But what do I know.
Minor 5. Prices.
Yeah. Would be a dream come true to a make a profit off of any card the bot has to offer, but can't brag too much. Some cards are just too expansive, sometime even more then market's prices. Since bot pays like 0.22 for a card it then sells for 2, would be nice to have some better pricing. Also I believe that it's contributing to "510k items" problem slowly, but it's still a humble brag from me.
Minor 6. Trades crushing.
Yeah, sometimes this, sometimes that. No "eligibility for trading" confirmation, err 22, err 16, etc. Pretty sure it's Steam's problem, nothing to be done here. Just had to say this.