I often link to Adventures in Homebrewing. Their starndard url is http://www.homebrewing.org/. I simply add ?AffId=500 to any page on the AIH site to create http://www.homebrewing.org/?AffId=500 and when someone clicks the link a cookie is placed in their browser. Any purchase made over a certain period of time (i think it is 30 days with AIH) will give me a commission on the sale.
More examples:
Here is a 1lb bag of Briess 2-row from AIH
-Not an affiliate link: http://www.homebrewing.org/2-Row--Pale-Ale-Malt-1-lb_p_3724.html
-Affiliate link: http://www.homebrewing.org/2-Row--Pale-Ale-Malt-1-lb_p_3724.html?AffId=500
MoreBeer is another site that I use:
-https://www.morebeer.com/ vs https://www.morebeer.com/index?a_aid=HopHeadHardware
When someone clicks on one of the affiliate links a harmless cookie is placed in their browser that triggers the site to say "hey, this person came to our site via HopHeadHarware." We get a small commission from the sale and it doesn't affect the price of an order in any way. It could be argued that affiliate commissions are calculated into prices but it can also be argued that affiliates are a good way to boost sales numbers while keeping overhead low. That results in a more profitable business that can provide better service, pricing, and selection to their customers.
Some Reddit users that participated in the discussion were concerned about biased reviews and their concern is valid. I think the majority of the homebrewing community is above that. I know that HopHead Hardware never recommends products for the sake of sales via our affiliate links. Getting caught doing that would tarnish our reputation that we are just starting to build. Naming names would not be cool but we recently dropped two affiliates due to reports of them screwing their customers by inflating shipping charges to outrageous amounts at the same time that they were running a big sale.