The spec. tag is in the left, outside pocket. If you could see it, it would show the size, the DSA number, the manufacturer and the contract date. But I can tell you it is almost certainly an issued Alpha. The zippers are the key to my opinion.
Truthfully, the jacket appears to be in pretty good condition. The knits look fine, and they are almost always the first part of a nylon jacket to go. If it is a size large, and it is in good condition, eighty bucks might not be too bad of a price. You won't be stealing from the seller, but he won't be raping you, either.
Finally, E-series Alphas were very well-made, warm jackets. I think collectors don't get excited about them because quite a few were produced and they lack some of the charm of the older, A or B series grey-lined MA-1s from the fifties. But if you want a good, tough, warm, Vietnam-era flight jacket....E-series MA-1s are a good bet.
By the way, if that jacket is an early-seventies, Alpha MA-1 in size large, it is exactly like one that was given to me in 1976. That old MA-1 was my first real flight jacket and main reason why I love them so much now.
AF