I can understand why the buyer might have felt disappointed, but that does not justify his conduct.
OP was paid to tank a mythic plus. What that obliged him to do was as follows:
- Complete the run (he did that)
- Perform his role to the expected level of someone with the experience and gear he told the buyer he had (he apparently did this)
In addition to meeting those requirements, he also made sure to bring a flask and food to help to ensure the presumably implied desire of the buyer (namely to finish the run in time).
What would have made it a "scam" would have been the following:
- If the OP had falsified his qualifications (eg lied about his ilevel and/or experience tanking M+)
- Intentionally underperformed during the run
- Left the group before completing the run
While it is understandable that the buyer had an expectation that the run would beat the timer, I would argue that this was not reasonable one. There is no way that one person can guarantee the success of the endeavour, and unless the failure was specifically because of the tank, then the OP has no further obligation to the buyer regardless of what the buyer wants.
If the buyer expected his money back in the event of not making the timer, that would be his fault for:
- having an unreasonable expectation
- not being explicit about his expectations with the people he hired, or that they would be obliged to return the money in the event of not making the timer
The only scam in this story is the buyer attempting to get his money back.
I agree 100% with the OP. I think he was perfectly reasonable in accepting the gold and doing his best to help the group. I don't think the buyer had any right to expect his gold back. The OP spent gold to buy flasks and food, the OP wasted his time. Had the buyer stated up front his expectations in the event of a failure, then that would be a different story. In fact I believe there would have been no story at all, because the OP would likely not have agreed to such terms.