Just because they don't make a profit doesn't mean they don't have to collect sales tax. When Walmart sells AA batteries as a loss leader, they don't get to not collect sales tax for it just because they used "all the money gained [(and then some, out of their own pockets!)] for either shipping or purchasing the batteries".
It gets really complex, in fact: the warranty replacement is only tax free if the warranty was a taxed line item during the original sale. If you make repairs to something, and you pass through the costs of the object to the person hiring you, you are generally considered to be a "retailer" and are responsible for collecting sales tax (which explains why you see wholesale discounts being given to large classes of professionals, from plumbers and carpenters to interior decorators).
That said, I am not claiming that the sales tax is the issue here: I'm claiming that this is a complex situation with a lot of intermingled laws and service terms, and that it is not at all clear that these people are running something that was entirely kosher and should de facto be supported.
People seem to have a thirst for PayPal's blood, and are totally ignoring (or, more favorably, simply not realizing due to lack of knowledge) that this was a somewhat sketchy, certainly risky (from a credit fraud perspective), and probably even illegal operation; and it makes no matter whether it involved feeding children or sick cats, or whether this is a computerized algorithm that flagged it or a person: the reason for the flagging, and for the blocks, actually makes a lot more sense when you examine the whole issue.