On some servers this plugin is used on, they don't offer refunds for certain pstones they have. No big deal, unless you accidentally place a very expensive pstone, and it drains your economy account of all it's money.

I suggest safeguards to prevent accidental placement of pstones:
a) A confirmation message, only activating such block as a pstone if you agree that you are placing a pstone. "Place (pstone name) and credit account (cost of pstone)?" /yes /no could be answers to that.

b) A time limit feature, offering refunds to chosen pstones within a time limit. Accidentally place a very expensive pstone? Just lift the pstone within (time) and receive a refund.