Well, first you need to find out if your lfs had any problems in the past. If he did what did he do to try and solve fix the problem
What I mean by that is did he clean out his holding tanks, or displays. If he had problems and did nothing, I surely would not purchase there.
The shame of it, you will just have to roll the dice. If the speciman looks good, and you can trust your lfs in the fact that they did not have any problems you should be ok.
The other problem is the clam if infected can look great before hand, and then all of the sudden turn bad very quickly. Best of luck, and if you do decide to purchase post a picture and let us know how it goes. :smokin: