I’ve read a lot of horror stories where Amazon has randomly closed people’s accounts for different reasons. Fair enough – many of these are due to breaches of their terms and conditions (e.g. failing to properly disclose links, not using the appropriate images and links provided in the affiliate dashboard, buying from one’s own affiliate links, etc.) but yes, if you fail to comply by their rules, you’re at risk of being shut down (and losing all the commission you’ve racked up). SO, don’t be a dummy, read the terms and conditions thoroughly and make sure you’re not breaching them.
In February 2000, Amazon announced that it had been granted a patent on components of an affiliate program. The patent application was submitted in June 1997, which predates most affiliate programs, but not PC Flowers & Gifts.com (October 1994), AutoWeb.com (October 1995), Kbkids.com/BrainPlay.com (January 1996), EPage (April 1996), and several others.
Always disclose your affiliate relationship. Most visitors will probably understand that graphic ad will lead to your getting paid, but if you write a review or use an in-text link as a recommendation, you want your readers to know that may lead to compensation as well. This ensures you retain transparency and trust with your readers, but also, it's required by the FTC's endorsement rules.