My credibility is more important than a commission.
Successful designers are often targeted by manufacturers by the offer of free product and/or monetary compensation in appreciation for publishing with, using, or promoting a product. I have never chosen products based on whether or not the manufacturer pays for publication, as credibility is important to me. I select supplies based on quality alone.
It's a matter of trust
Those who will promote anything for the promise of payment (or free product) can cause readers to view affiliate links with suspicion. I occasionally include an affiliate link for a product or service, if it is something that I use and like, but these are few and far between. My approach is, if I like it and am going to provide a link, it may as well be an affiliate link--as long as it is convenient. I would rather have credibility than a commission. The majority of the links I provide are simply for your convenience and I want my customers/clients and readers to know that they can trust my recommendations.
What I do
As a designer I am often provided with free products, which I use if I find them to my liking and they are a quality I feel comfortable endorsing, either passively by my use or actively via recommendations.
I can’t be all things to all people so I occasionally partner with artsy friends who sell some of my favorite supplies, which means if you buy anything using certain links I may get a share.
If I like and use a particular product and that manufacturer offers a pay-for-publication or designer support program, of course I will participate. I would be foolish not to. However, the existence of such a program does not influence my decision to use a product.
What I don't do
Regardless of whether a manufacturer offers payment or how I receive a product, either I've purchased it or received complimentary samples, I will never passively nor actively endorse it if I find it to be substandard. I cannot be bought.