Don't intend to sound holier than though, but my infiltrator is now 4L7 and I rarely pass up a bd if I have the opportunity, easy kills with disease and dot poisons... then again, I'm templated so I don't worry about it.
As for the reaver, what levels are we talking about here? if you're a 50 reaver trying to take out the bd... TWF 1 - 3 and 50 flex + slam should easily take out a bd.... simply drop twf, slam, leviathan X 3 ... that should get it.
Any level less than that, watch the bd and lure him through some items that require him to use some power... power isn't easily gained on a bd unless you have pots or items that give power charges... Power is easy to remove them from if they aren't paying attention. Many suppression bd's get too wrapped up in the 1-button-wonder-syndrome, and forget about the limited power pool. Many darkness bd's you'll have trouble getting close to if they're good and/or botted.
Your problem is one that requires much more information than you have given to help fix if it is possible to fix.
- Geotide, I could list a buncha characters but 1 does it.