I really feel like there should not be a fee to be honest, and I know this way the /pwarp option would kind of be extinguished ( for shops at least ). I can see this help the server but if there is going to be a fee for every purchase I feel like everyone will just use the more popular /pwarp shops still if there is going to, I know I certainly will not want to pay a fee if I know something is in stock.
The major plus I can see is being able to find specific items quicker, also finding items that are usually sold out in the major shops. But still that fee.... I don't know, testing will tell, I probably would not use it just because of the fee.
As far as the chest shop owners covering the fee, this may help the idea but also take away profit from sales especially from the new smaller chest shops starting out for new players. I feel like they would not want to help pay the fee because they are struggling to make their chest shop a success with the small amount of money they may have.
Overall +1 for the idea ( still not Vshop and I would prefer that any day over this ) It will help sales for the big chain /pwarps right now.
-1 for the "fee" or "tax" I feel that new players will have a harder time trying to start chest shops and make money when big pwarps are covering all fees.