If yes, the author’s conclusion is valid, as the customers knew they had received extra change and dishonestly kept it. If no, then the author’s conclusion is invalid, as the customers did not know they received the extra change and could not have kept it dishonestly.

Irrelevant—the study’s sample is limited to customers who used cash for their transactions.

Irrelevant—whether the customers self-describe as honest does not affect the author’s characterization of them as honest.

Irrelevant—the conclusion of the argument is about how most of the customers did not return the dollar and therefore behaved dishonestly. The author doesn’t make an explicit claim about those who returned the dollar, or their intentions in doing so.

Irrelevant—the author’s conclusion is only about this particular study, in which customers were only given an extra dollar.