Amazon.com Inc. is offering independent merchants on its platform marketing support, product reviews and prominent display. The catch? Amazon gains the right to purchase a merchant’s brand at any time for a fixed price, often $10,000.

The program—which allows brand rights to be bought for a fixed price on 60 days’ notice, according to a contract seen by The Wall Street Journal—is part of a push by Amazon to obtain a stable of exclusive brands for the platform. It is the first selling program that allows Amazon to obtain direct...