Hello,
I am not certain if I understand what you are asking…
Do you mean that a customer can only order from one vendor at a time?
If not, please clarify.
If so, no- we do not have this built into WC Vendors. A customer can add items form many vendors and checkout in one cart. However, the commissions due for each vendor is either split at checkout and disbursed, or shown as “due” , depending on which payment processor you use.
Someone shared this code at one time ( I have not tested it) which will supposedly prevent customers from ordering form more than one vendor in a cart: