They essentially do. De jure each DT member has some degree of autonomy and permitted to do whatever he wants. However, de facto there is a system of precedents which is enforced by trolling the "inappropriate" individuals as well as using other shady practices against them. That is corruption as is, only insane individual would deny it.

There is no way to verify that itn't so. So, the only way to guarantee absence of any kind of pressure is to entirely isolate all paid signature wearers from the decision making process.
Trust, but verify. Remove the conflict of interests and you won't need to think about how to settle it.