Not backpurged, and not great quality. However, you asked for a SS exhaust and that's what they gave you. Unless you asked for back purging (or it was promised in conversation), back purging is not something that would "normally" be done.
Did you do any up front due diligence on the shop? If they fulfilled their commitments and you can't point to a requirement that's not being met, saying that you're "dissatisfied" mostly points to a misalignment of expectations, unfortunately.
Now if you were shown example work and a "reasonable person" would say that what you got wasn't in line with what you we lead to expect, that's a different story. It doesn't hurt to ask, but I don't think there's much to be done. I agree with the assessment above that it's mostly cosmetic, so that's the good news. Headers, yes, I'd be a stickler on back purging and quality welds. Exhaust pipes are such large diameters that it won't make much difference.
