I only needed one more item to “unlock extra savings up to 15%”, so I added an extra item to see what the savings would be. I didn’t think the savings matched what was advertised, so I removed an item to see what the difference was (making sure to screenshot before/after this time). Turns out the price of 3 out of 4 items is the same after an extra 5% discount.
I roll with no tracking/cookies/accounts. I check out as a guest. Prices change depending on location and purchase history. The best pricing is when the site has never seen you before. This also works for things like ISP new customer promotions and stuff.