Well I would put that behaviorist down the road. I agree with lvoss that most likely this will make your dog more aggressive. Basenji's are very smart as I imagine yours is as well. I really suspect there is more going on here than meets the eye.
It is a mistake to use force to break a dogs spirit and it will have a negative impact. With that being said, it is important for you to assert yourself with your pet. From my reading, there has been behavior in the past that should have not been allowed. Now your dog expects things to go a certain way. These problems and behaviors did not all happen at once and will take time and patience to be corrected. There is no quick fix, and even if you do find a good behavior therapist, ultimately your dog has to respond, respect, and trust you.
I think you should first decide if you are up for the challenge. You need to find your dogs hot button. What I mean is something he or she really likes and will respond to. Once you do figure that out then use that as a training tool.
Many have suggested using a gentle leader for a dog that pulls you when you walk. I personally have started using one with my Basenji even though I have been successful at times to get him to heel without this type of lead. This lead will make the job much easier but please read all the directions, watch the CD Or DVD it comes with, and make sure that you handle the leash gently when using this lead. It does work effectively. After a successful walk, treat your dog. Use Cherrios, pieces of hot dog, or another treat but do it right then and there.
If you get this lead and it works for you, then take your dog out for a 3 or 4 mile walk at your pace. First your dog will love it. Second your dog will get good exercise that will tire him or her out and your basenji will be much easier to handle. If you can do this daily, you will not only improve your own personal health, but you will also find that your dog starts looking forward to this exercise and time with you and becomes more responsive. If you walk in a park where there are other people, it will also help socialize your pet.
Now I am going to say something that I will probably catch heat for. Letting your pet out in a fenced yard to exercise is not the same as taking them for a walk. You are not in charge when you just put your dog out in the yard to exercise. When you take him for a walk on a leash you are letting your dog know that you are in charge and in control. In the past when I have had a dog I was having issues with, I have even put then on a leash when I was in the house. I made them sit or lay down when I sat. When I got up, they got up. Even if you have to do it for a day or two you will see how effective it will be.
During dinner time, Kennel your dog. Feed him his food at the same time you eat if possible. Basenji's are great beggers as you already know. Since you gave in to his/her Begging you really need to let the dog know that they will not be allowed to continue. The best way is to kennel them during your meals and provide one of theirs for them. This does not mean your dog will completely stop begging, but if you help them form a different habit then they will start responding to it.
As I am sure you already understand, this is all about conditioning. From your own words you have conditioned your dog as to what to expect that he can get away with. Now you have to condition him to understand what is acceptable and what is not.
None of this is going to be easy so do not expect it to be. Sometimes things can get worse before they get better so expect that. All in all this is the time where you need to practice Tough love with your dog. Ignore the whinning, crying, and scratching when you kennel him during meal times. Do not feel sorry for him if you use a Gentle Leader as has been suggested and he tries to get it off. Practice Tough Love.
Hope some of this helps.
Jason