Extensions must be done in writing and there should be a fee involved. This is on the extension form. That's part of contract law called consideration. I am not an attorney, but the way I understand contract law is that the seller could not extend the option period without receiving some type of consideration for doing so. What is appropriate is somewhat vague. Some attorney's have told me for example $1 is not enough probably to be valid consideration....but then the question is if $1 is not enough, then what is? If the original option fee was $100 for 10 days, would $10 be enough for anther 3 days?...you only find out if you go to court.
There's probably more to the story, but in most cases I would think anything the agent is doing for either party would be in consultation with that party.
Talk to your agent about it. Tell them you want to be involved 1st before even any informal discussions or negotiations are done.