After locking out a commercial tenant for failure to pay, do I have to accept their late payment or can we simply re-rent.

You have to look to the contract's language on this to determine whether being 9 days late gives your the right to evict. It certainly may, but without seeing the lease, I don't think anyone here can be of too much help.

When you say "lock-out" did you obtain a court order or did you lock them out without an order? If you have an order and the lockout was done properly, then no you do not have to accept their late payment and allow them to move back-in. If you did the lockout without a court order, then the situation is a little bit more complicated. You may want to contact a landlord tenant commercial property attorney.