I prefer to pick my clams from the LFS so I can observe the mantle for pinching and light change reactions. Slow clams, folded clams not fully expanding for the light are a huge gamble, imo.
I recently took a chance with a sponsor of R2R, @
https://pacificeastaquaculture.com/
The 4 clams came in healthy, no pyramid snails, mantles opening to light, closing for shadows, and the bysis/foot area operational and not torn, all 4 have attached well. I am very happy with what they sent so I felt compelled to leave this comment here in case you are thinking about purchasing on line?
I have my clams basking under 250W Phoenix MH, and they are looking pretty good after a month without any of the typical clam issues.
DSC Reef was correct about what to watch for and how to respond. If you are dealing with a good vendor/lfs hopefully they will have handled any of the dip & pest removal chores before they pass the clam over to you. The only thing you should have to do would be to drip acclimate the clam to your water. I would perform a water change before you get the new clam so that you don't change your tank parameters soon after you add the new specimen.
A nice clam can be a great showpiece, I hope yours works out!