Just step on their shoes. Then glare at them why they block your path. Walk away.
Do the following and you will solve your problems:
1 At a distance if you noticed the agents, just walk your way pass them without giving any eye contact, even if they speak to you, just walk on;
2 If they ever block your walk, wag your finger and just tell them, don't block my way. If they don't, just shout louder, 'don't block my way'
3 If they ever have the temerity to pull you away from your path, shout at them 'don't you dare to block my way or touch me...I will report you for unlawful retention of others without their consent....'
4 Always be prepared to confront them if they ever try anything more than try to approach you or block your way. After a while, they will learn to recognise you and leave you alone.
5 If they use the excuse of doing a survey, just walk off if you are not interested. In most cases, they are obliged to wear their company uniforms as advertisements and it is easy to spot them.
Did that to the aia and prudential agents at some shopping centres and they never dare even to approach me...

I guess, their experiences with other people also taught them to be smart enough to avoid those who showed that they are not interested.