I would not buy any theme park tickets off of Ebay. There is no way to verify if the tickets are still good until after you spend the money and that could be too late.
That's just not something I would want to gamble on...there's too much money to lose to a scammer...not saying whoever this person is will scam you. But there are lots of people out there who will scam people. I would try to find tickets through other realiable sources before even considering Ebay.
The ebay seller with the coupon code has good feedback, and it's only 1.49 for the code, so there isn't a lot of risk there. Only thing is that the tickets expire at the end of the year, so you would have to be going before then. I wanted the 4 day/2 park tickets and that isn't on the list.
I was at WDW last year with someone who bought her ticket from an ebay seller. She got in one day (it was a multi-day ticket) but had trouble getting fastpasses and the like. The next day she was refused admittance. They discovered that she was not the person to whom the ticket was issued, etc. She ended up having to stay at the hotel all day.
Not worth it to buy the actual tickets. As for buying some coupon - maybe for $2. I would be careful about making sure to pay for the auction through secure channels that you login to yourself (not links sent to you). I don't trust people who sell stuff like that.