I usually don’t try using coupons since many of the codes shown on websites don’t work, but I feel bad for not trying hard or smart enough. I’ve heard good things about Retailmenot, I haven’t tried it yet but I wondering if there are privacy trade-offs.
Now they are all really scammy. I haven’t found a good code in years. All those sites do is forward you to the site with a referral link, if you buy something, coupon code or not, they get paid for the referral (and possibly future purchases you make).
Best I can suggest is to attack their business model. Open those sites in a private tab, copy/paste the codes to your normal browser.