99% garbage. They almost never work. The majority of sites generate fake ones.

If I'm buying something off the internet, after I've progressed to the point of checking out, I'll give 10 minutes to trying to find a coupon code for my purchase. Probably 90% of the time, the codes are useless, expired, or just plain fake. I figure, I'm already on the internet, I'm not it that much of a hurry to click 'purchase', why not do a cursory search. Might get a couple dollars off for my search time invested.

The usual measures, like avoiding their browser extensions and cookies, should keep you in the clear for the most part. The last time I had a code from Honey, Retailmenot, or Groupon work for a major site like eBay and Amazon was maybe in 2021. Stopped trying later that year. They've mostly cracked down on it in favor of automatic discounts.