The correct answer to this open question is the following.
Although there are no options attached, we can say the following.
What I would do is to allow employees to select the vendors and products to sell. However, for this action to be successful, I would establish clear criteria to be followed by employees so they can select from that criteria what the can and can't offer.
I think a certain degree of autonomy is important for the employee to be better involved in the selling of products. It is like taking into consideration its skill and abilities and let them use them in the workplace. But as I wrote above, employees have to have some parameters in which they can decide the best option. Those parameters will be approved by top management.