When using the price parameter in the config file, a block can be placed without any money being taken out of the players bank account, and when removed money is credited?

I cannot replicate this problem, can you provide exact steps?

I installed PS as per normal. I then edited the config.yml file and added price: 100 on each of the stones. I restarted the server and then a block can be placed without any money being taken out of the players bank account, and when removed money is credited?

I am using iConomy in conjunction with this mod.

Yep, that's the one. However, they are being credited when it's removed.. so they effectively gain money..

So money is never taken out anyones account?

I really don't see how they can place a field and not be charged money. What version of iConomy do you have?