If I kept/bred boas, I would weigh having this done, and if it were a reasonable price per animal, why not have it done. Problem is, when if a good chunk of your breeding colony comes back as carriers? Are you going to cull them? Up to this point, you really cannot blame the person you got it from if you have an asymptomatic carrier, so what will you do? One of the biggest barriers will be that folks do not want to have answer this question.
Which brings up another elephant in the room. Quite a few respondents said they wouldn't trust the seller's test results and would get their own done on their boas shortly after they arrived. As was pointed out, BP's most likely would die within the QT period if infected with IBD while boas can carry it for years.

So, hypothetically, what if your new boa does pop up as a carrier? Naturally you inform the seller, and if you're dealing with an ethical seller you will be able to return the snake. The seller should lock down his collection, test every boid, cull and/or isolate infected snakes, etc. BUT the herp world attracts its share of scoundrels, people who won't accept a return and who will keep selling - or you may even see the IBD-positive snake you returned up for sale again.