A is incorrect, because it would strengthen the argument against buying an extended warranty. That is, you already know from the original paragraph that salesmen want to sell extended warranties, because they get more commission. Therefore, the only possible interpretation for the phrase "poor value scheme" is an extended warranty. Taken together, you can infer that if A is true, the salesman is trying to sell you an extended warranty that isn't worth it. That argues against getting the extended warranty.
C Definitely strengthens the original argument against extended warranties. If the retailer is smart, he's going to price the extended warranty at a point that exceeds the average cost of repairs.
D This makes the warranty less useful - hence, why would you buy it?
E Again, this makes not getting the warranty less objectionable, and is thus an argument against getting the warranty.
Finally, B. I think there's a hidden assumption here: if the majority of people don't get their electronics repaired, you have to ask why. Maybe it's because they can't afford the repairs because they don't have the extended warranty. So this would weaken the argument, because it would put you, the supposed buyer of the extended warranty, in the position of being "above the average", so to speak. Does that make sense?