Steam Trade Card Farm With Alternative Accounts

As most steam users do, Im buying cheap games to the farm their cards.

That's a bit of an overstatement 😆😅
I think it would be more accurate to say a considerable portion of SteamGifts users do that but this community here is in no way representative of Steam gamers in general.

I suppose it depends how many gifts you're sending to your alts (I've heard about people getting their buying privilege temporarily suspended for excessive gifting) but I think you should be good.

Just don't mess around with regional pricing.

But I dont know can I get ban cause of this.

If you do something stupid - yes. Key is number of requests to steam servers from one IP. If you use some kind of automation and spam steam servers with hundreds and thousands of requests, especially during sale, when steam servers are overloaded even without your help - yes, you can get banned for it, I've heard of such cases. If you do it manually? Well, I doubt you can get a ban, worst case scenario - they will block sending gifts from your account, but if you pay with real money, not with steam wallet - even that is unlikely.
Of course, all of the above is only my opinion, since I don't work at Valve.

I only know of one case who got his accounts locked, he had a bot farm with more than thousand accounts.

I've always been on the fence about doing that type of farming for fear of it looking a bit too suspicious of an activity to Steam support, and general laziness to be completely honest, so I've always limited myself to only farming cards from keys on my alts, plus event cards of course.
But I'm curious to know how it turns out for you, for science of course, it definitely isn't that I'm considering the idea. So, let me us know if it goes well for you ;)

in my opinion it will depend on the number of accounts you make, like 10 that may work for you, but if you do hundreds of them it will cause a huge problem and you will get banned.for sure ¯_(ツ)_/¯