Update: I finally got ahold of the guy. He was very apologetic, and said that it was really for 1 maxima, and admitted that the person who built the ad for him (must be one of those E-bay consignment businesses) made it appear to be all 10 of the clams he was selling. Thanks for second-guessing this for me. I'd have been a little hostile when I opened the box expecting to get 10 and found one! Anyway, we talked for a good half hour, and he made me another offer involving what he called "show quality" 4-5" clams--2 crocea and 1 maxima--for $70 including shipping. I'm not sure exactly what to do, since I still have a net budget of $0.
Anyway, I did get an email back from someone who did buy something from him (his only feedback) who said the packaging and shipping were very professional.
In the mean time, I'm going ahead with the sale of my queen and singapore angels--something no one in this thread will want--to make way for a clam in the future, not to mention a star or two.