It is incredibly hard to win as a merchant in any kind of dispute. The burden of proof is on the merchant not the customer.
The merchant pays a fee regardless of the outcome, and if you end up with more than 1% chargebacks your account is cancelled. The net effect is that any merchant who is doing this on a regular basis won't be accepting credit cards for long.
Additionally, the system is so far in the customer's favor that it's causing a fairly large fraud problem for merchants. It's bad enough that my small business won't accept credit cards for very large purchases unless the customer has a history with us.