I'm no expert on fish, but the tails look a bit different to me. The third dip in the tail fin on the second one is sharper, more like a notch. The first one's is more curved. They look very similar, but I think they're different. Like I said, though, I'm no expert.
Hector - Male Delta Tail
it could be the different position, am really worried =[ IF this is my betta, well there goes $40 down the dumps and my mother will get mad, and i will be upset. i really need help D= i feel like telling hopdiggity but she never responded to my last message =[ and am really nervous that she will get mad at me
The second fish has much less red than the first, it looks to me. I wouldn't worry. Sisters from the same spawn can look very similar, and I highly doubt a breeder that of any worth would try to dupe you. It's too big of a risk and would reflect very badly on them if they were found out. I would say wait and see when you get your fish before you make any accusations.
they're spawn sisters, it looks like. the seller often gets lots of bettas from the transshippers in Thailand. i've seen brothers and sisters on her AB page often! don't worry, she's not tryin' ta cheat you. :V