Post the name of the seller if you can, so we'll know who to avoid. A common trick that dealers in counterfeits use is to immediately refund the money of anyone who questions them, in the hopes of avoiding detection in the marketplace. (Like the guy with the fake GP grips). I'm guessing that since you're in the UK, this vendor was probably ASIA based and willing to ship worldwide. That's warning sign no. 1. In fact, while I'm at it. Let me post a few of my rules of thumb for avoiding counterfeits while buying on-line. Just the basic basics, not a primer for spotting fakes, which gets complicated.
1. Never buy anything from vendors in Asia. Meaning China, Korea, Hong Kong, Singapore, Taiwan, Thailand. Japan sellers are okay for pricey JP market specialty stuff. Australia is okay. This tip alone will eliminate most of your problems.
2. Never buy anything based on stock photos unless a seller is selling NEW from the US and is reputable. Always look for actual photos on Ebay.
3. Never buy anything from new, lesser-known, pop-up .com vendors. With so many big, known vendors like 2balls, golfgalaxy, golfsmith, why risk these unknowns?
4. Never buy anything from a site displaying bad or broken english. That's a tip-off that it's really China based or using shills in California as drop-ship proxies.
5. Be aware that counterfeiters like to knock off high profit easy-to-make single items, not low-profit hard to make items. That means a Cameron putter is MUCH more likely to be faked than a set of Ping irons.
6. When in doubt, consult the manufacturers lists of approved vendors. Call them and ask. They won't tell you who's on the "naughty" list, but they will confirm is someone's on the nice list.
Hope this helps somewhat
Also on eBay, ask the seller for a serial number. In my experience with Callaway a quick call to customer service and they'll verify the serial number for you.