Buying 18650s can be fraught with danger as there are many charlatans selling cruddy product. I would avoid Amazon unless it says sourced from an Amazon warehouse. If Amazon hold stock then the company/product is normally more reliable. Amazon just want to make money and if their 3rd party supplier attracts complaints etc. Amazon will drop them as they want your money not hassle.
Or buy from a battery distributor in the UK which offers carrier delivery so you don’t get into any grief with Royal Mail deciding they don’t like the packaging. Also buy on your credit card so you get Consumer Credit Act Section 75 protection. That way not only is the vendor responsible for making good if the products are cheap copies that don’t work, it means your Credit Card company are JOINTLY and SEVERALLY liable. So if the company wont refund or replace then the Credit Card company is responsible for 100% of the cost.
Buy a good brand name and don’t go for the biggest capacity you can see as even the good companies can be a bit iffy with specs!
Myself, I have acquired used laptop power packs and stripped them for 18650 cells. Expect 75% of the cells in a pack to be acceptable with a few gems and some that are knackered. Sometimes you strike out, the last pack I dismembered had 12x 2800mAhr 18650s and they’re all a bit rubbishy TBH.
See https://reflector.sota.org.uk/t/using-18650-liion-cells/20958