You have a decision to make and you did. Vendor A has practically won in all aspects. The next step is to award the contract. You decided to pay them a visit and shake hands. They went all out and entertained you thoroughly. At the end of the day, you told them, everyone toasted and was happy. You came home. There was nothing inappropriate. Those entertainments did not influence your decision.
There was a power asymmetry and both sides knew it. You exploited that asymmetry. That was the beginning of corruption, not just for you, but for your whole organization.
Many senior managers enjoy the authority that came from their position. In fact, I observed that the majority of them are really motivated by power: the ability to control others. Quickly, they learned the special treatments that come from having power. Then, they demanded those special treatments: not wait in the line, a personalized service, extra portion, etc. When not getting them, they wielded their power.
The decisions influenced by these factors are usually sub-optimal. Soon, these plays filtered out the best decisions or the best people. What’s left are those who are willing to play the game that is not meritocratic, at least not 100%. At the end, the whole company lost its edge and competitiveness.
Be aware of the asymmetric power structure. Use it for the company, but not for yourself. It is hard to resist, so you will need to be extra vigilant.