This strengthens the argument. It strengthens the author’s assumption that the issues which tend to occur after the normal warranty period expires are not more costly to fix than simply paying for the extended warranty.

This weakens the argument. It says that the extended warranties are not costly, suggesting that purchasing one may not be as big of a loss as the author implies. If extended warranties are cheap, the amount that one is “generally better off” is reduced.

This does not affect the argument. The author says that consumers generally should not buy extended warranties—this implies that there may be a small minority of consumers who actually do benefit from the purchase.

This does not affect the argument. This is not really new information—the argument already describes extended warranties as “warranties that extend beyond the manufacturer’s warranty.”

This does not affect the argument. Our concern is not with how stores benefit from selling extended warranties, but how consumers benefit from purchasing them.