When buying items for the casino, any item that is unavailable because of not enough money is grayed out properly. However, when you spend, the list of items that you cannot afford is not updated until you go "back to groups". An example is attached.
In that one, I had over 5,000 chips, and the vending machines are available. I purchased two trash cans, lowering my chips available to below 5,000. When I paged back to the vending machines, they were not grayed out, and I was able to attempt to place them (resulting in an "Oops..." message).

This isn't an urgent fix, but it is probably something to be addressed before you go "production".