Vacations are typically forbidden and would immediately be seen as a bribe. This has led to all kinds of things that are practically vacations but officially are business (such as: conferences in sunny resorts, conferences that take three weeks and so on). Other 'entertainment' can come in many different forms and if not disclosed can get both parties in hot water.
On the whole, pay your own way, do not accept anything that might be construed as a bribe afterwards (so no discount on that shiny item from the company you are deciding to do business with, or not), no gifts over a very low dollar value and in case of doubt clear with legal/linemanager/accountant, transparency is key here, just a failure to disclose can turn an otherwise innocent thing into a potential bribe.
It's really not all that hard to keep your nose clean.
It is not unlawful to offer incentives to the company itself in order for them to make a deal. In fact, that's effectively how most deals close (the incentive is usually simply monetary and takes the form of a discount). The problem here is that Kail abused his position as an agent of Netflix to profit at their expense.