Many youtubers and friends share their referral codes/affiliate links, saying you will get bonuses, real money, or free spins. but I wonder if casinos give extra help or benefits in some different situations.
For example, when someone wins a big multiplier and multiplies their account by 100x, then some casinos take a long time to process the withdrawal, or they may not even give the money. however, some say that if you sign up using a good affiliate or influencer affiliate code which have huge audience, then you won't face these type issues. also, if you promote the casino using your referral link, they might not hold back your withdrawal because you helped them get new customers.
is this kind of things is considered shady practice, or is it considered fair in the online gambling world?
Err no, those don't happen afaik. Affiliate links are there to benefit whoever gave them out, not those who are using them. Otherwise, you would've expected a lot of bots to be farming the hell out of that kind of mechanic. Well even if it was a mechanic like what you said, I don't think casinos would implement it since in the first place, withdrawals are withheld because they're trying to trace any possibility of the funds the account has being used for AML. Plus, it's mostly an automated process of gathering data, and then a person just has to check whatever the results are and if suspicious would they only then do a much more intensive background check.
I don't think a shady practice between user and casino is even possible in the case of online gambling really. Well, maybe fake reviews but those are hired hands compared to natural site users.