One of the things I constantly see when going to BBQ's is people completely cremating chicken. It seems like such a shame, but you can understand why they do it. There is this constant fear that the chicken or any BBQ'd food is under cooked, so to feel "safe" the food gets "cremated".
If you really want some nicely done chicken on your BBQ you have to be patient, don't flame the chicken unless near the end if you want a crispy finish. A little trick I use is to season the chicken with black pepper and salt, then wrap the chicken in Sage and Rosemary. Wrap it all in foil and place on the BBQ, you'll be amazed by how fast the chicken actually cooks this way!
After about 15 to 20 minutes open the foil and check on your chicken. I have a nifty little gadget I bought in Sainsburys, its a fork you press into the meat which tells you if its properly cooked by measuring the temperature inside. When the chicken is cooked take it out of the foil and place straight onto the BBQ grill to get that nice crispy BBQ finish. Use the juices from the foil to pour over the chicken and enjoy.