If I block a person, will he be able to purchase from me? I want to avoid an order from a person with a Behaviour which I don’t like.
With Fiverr is always hard to predict if things will work as expected, but theoretically a blocked user shouldn’t be able to send you messages or place an order with you, although I’ve seen people reporting that they were still able to place orders after blocked.
I believe it might be more effective to tell your potential buyer that you don’t want to work with them. You can either be upfront and tell them you don’t think you’re a good fit, or just tell him you just got a big order and won’t have time to work on theirs.