This will depend entirely on your product and operation.
Remember in your swabbing, you are looking for problems. Dont be afraid to get a positive result during your swabs. Too many times I see facilities shying away from "dirty" areas. Its best you find a hot spot before the customer does through a recall.
I second this. In a recent chat with a BSA auditor who contributes to their Listeria guidance, she mentioned focusing on trying to actively find listeria rather than trying to 'prove' it isn't there. The liklihood is that listeria, for example, will be somewhere - identifying when/where and taking appropriate actions to protect the food and end consumer is the best course of action, in my opinion.