Thanks for the tip, Simon. I do know about Wai's. I visit his store every week, he has some nice candy for sure. But I have to caution you about Wai's and clams. He sells some good stuff, but, sometimes, well .... I don't really want to get into it, but let's just say "caveat emptor." His clams don't necessarily fare any better than from any others. He'll happily charge you $150 or more for clams with, that upon inspection of the clam when you get it home, has evident damage to their byssal gland. I unfortunately speak from experience. As I'm sure with many LFS, you have to trust your own instinct about how much risk is associated with a certain purchase. Some things are fine ... some things may not be, despite appearances.
Unfortunately with clams, it's very hard to guage what that risk is, because, they tend to look "100% healthy" up until the point that they die. Look fine one day, boom, next day they're gone. I'm not exaggerating. It takes a very keen eye to spot trouble early on (usually the easy way to tell is to look at the byssal gland .... not many LFS will let you do this in their store, however).
To be fair, I know of several
T. derasa clams that have come from this store that have fared well over time.
T. maxima and
T. crocea have horrible survival rates in my opinion, doesn't matter where they come from. The smaller they are, the worse it is. The problem I had was with
baby clams (2" and smaller -- some as small as 1"). I knew that the odds were not good going in (this is why they tend to be cheap too), and despite my efforts, the odds were correct this time around. I fed copious amounts of DT's ($50 per month ... I was not kidding when I said "I joined the DT's diet and in six months I lost $300." The end result is the same: I have about $200 worth of shells now, and about $300 worth of empty DT's bottles.
From here on, I'm staying away from baby clams. If there is a "next one" for me, it will be some 3" - 4" monster. And if it comes pre-attached to a rock, so much the better.