I believe IBD isn't as common as some people think. Honestly I keep my boas and other pythons in the same room (after proper QT) and I believe that it's a possible risk that any owner takes that owns both boas and pythons in close proximity of each other. My advice is to search for an interesting IBD thread that Skiploder wrote (I couldn't find it but maybe someone else can) as it's very eye opening and informative and buy only from reliable/reputable sources. I would never buy a boa off of CL for this reason (as well as other possible health issues) as I will not risk my current collection or my boyfriend's. On a side note I've read that (some) boas can carry IBD for years without showing any symptoms so even the ~3-6 month standard QT period might not be enough to safe guard your established collection. Hence why I say it's a risk that any boa and ball/python owner takes IMO.