High pressure sales techniques are awful, and they exist because they work. I don't think having to say "no" 50 times is reasonable, and it makes you feel like an asshole just for not being an easy mark that can be pressured into buying something s/he doesn't want. I've learned to close the door in the face of over-aggressive solicitors, but I know people who have trouble with it, because it's objectively rude to do something like that. The only reason I find it acceptable is that these sales techniques are intentionally designed to exploit people's hesitancy at being rude to other human beings.
So yes, it's common practice. That doesn't mean it's not a practice that is loathsome and bad for society.
Note: I think strong arm is a completely reasonable description of this. The sales person offered multiple carrots, and then upon being rebuffed, brought out the stick (keep in mind that the context is someone cancelling on the last day of their subscription):
>Chaitra: Devon, you have purchased a subscription with annual commitment, since you wish to cancel the subscription before the end of one year period, you will be billed 50% of your monthly rate for the remaining months in your annual commitment as early termination fee.
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>Chaitra: If you pay early termination fee, you will not be able to use the product, however If you continue with the subscription with 2 month free subscription you will be able to use the subscription and also get two months free subscription. In this case, I would suggest you to take an advantage of two months free subscription.
This wasn't a good faith misunderstanding, this was a situational script aimed at maximizing retention in the particular context. This is a lever that is being intentionally applied to cow people into buying an extra year of a service they don't want.