This is highly localized. I can only speak for North America in my answer, and even then it depends on the culture of the business & industry. That being said...
I wouldn't call specific hand gestures dominating necessarily, but they are part of a 'game' that some people play. When they experience a familiarity with a situation it gives them more comfort and confidence. For example, if you step into a car dealership, a lot of salesmen will behave the same way: shake hands with everyone (including each other), ask the exact same small talk questions that they can give pre-canned comments on, etc.
This may become a problem for you if the level of comfort with what's going on is asymmetric and the conversation is inherently adversarial such as a negotiation. Pushy salesmen & certain business people strive for this. It helps them steer the conversation their way and makes sure that the whole thing happens on their terms.
The only way out is to break their 'game'. If they are taking you out of your comfort zone, you should make sure they are not sitting perfectly in theirs either.
I learned how to avoid shaking hands from a guy I used to work with. He just never shook hands with anyone. Period. Maybe it had to do with the SARS epidemic, but it somehow worked. Let's say the stereotypical frat boy salesman says "Hi Valera, how you doin'?" and reaches out his hand. Your answer would be "Yeah, great, thanks!" and you just stand there with arms at your side smiling. You should be very outgoing, friendly, and cooperative not to give a 'cold' impression, but a the same time not play into his prepared script. At this point, their norm of the conversation is challenged and they will be forced to talk with you differently.
Pat on the back
Similar to the handshake, you should make sure that they feel uncomfortable doing it. Don't shrug it off, but step a little further away from them after they do it. Alternatively, make sure that their action results in a pause. It's not the reaction that they are expecting and it breaks their script.
This is all sales 101. In my experience, technical people are not very good at this sort of thing. However, it's a skill like any other that can, and should be learned. Don't let people play their pre-canned scripts with you when they are trying to get you to agree or commit to something. Some do this sort of thing very well. Physical gestures are just an extension of their scripts that are easy to thwart.