This is very common in many cultures and drives many of us to madness. But statistically, it is a proven negotiation technique for closing. This negotiation technique is in play if more than a few asks are made in a short period of time, or when no new information has been given that would potentially change the offer. The reason this tactic is used, regrettably, is that it works for the people who use it: they can wear people down. This is not a recipe for a durable deal or long-term relationship.
“Do you want this product? It will solve the problem you stated. All you have to do is sign here. Are you sure? You just told me you have a problem… This is the solution… Sign here… This product will fix your problem…”
The way to oppose this tactic is to just say no and call them on it. If the badgering continues, simply walk out. Politeness makes us stick to compelling, intelligent, or otherwise attractive people. Learn to walk away. This tactic is a signal of disrespect in most cases, or naiveté in others.