I had a very good experience with ebay seller collector52.
Looking at her items, I see she is not primarily a poster dealer. However the price was very reasonable on a lesser poster (Bye Bye Birdie insert - Christmas gift for sister)
She was very responsive on e-mails. She shipped the poster xpresspost from Canada the day I won it, which was more than promised. Best of all, the poster was rolled and triple tubed. Probably the best packing I have seen from someone who doesn't do this daily.
positive rating.