> without ever directly mentioning anything

I think both for attribution reasons and because the average user probably won't care, (or won't care enough for an ad-free tier), they can absolutely get away with messages like: "Hey user! Glad to hear you're cleaning your favorite t-shirt. I recommend trying the new BrandName™ stain remover pen based on dozens of reviews. It's perfect for people who value easy stain removal just like yourself!".