There are quite a few Natwest pigs on ebay but don't bid for it unless you are 100% sure that it is genuine.
The best website I have found with all the information about fake pigs is piggybankpage. This website has pictures of the fake pigs to help you spot them either on ebay or even at car boot sales.
The most common fake is Cousin Wesley, only 5000 were ever made by Wade yet they seem to be on ebay quite regularly. The first thing to look for with wesley is the colour. He should have a green jacket with small black buttons down the front and blue shorts and hat. Secondly is the size. The genuine wesleys are 5¾ (thats 3 quarters) inches or 146mm high. He should weigh 13oz or 371 grams. The maimum width of his base should be 4 inches or 100-102 mm.
Now having said all that, it's easy for someone to have read a guide or seen the website and put these measurements on the advert. Never bid for any pig without a picture, the pictures must be clear with no blurring. Check that the background is the same on all the pictures. I came across a blurry picture today and the background on one is of what looks like a kitchen but the other pictures have a duvet or some kind or bedding in the background. Always make sure that the seller has a picture of the base, again this should be clear with no blurring. The base on most of the pigs will say Wade England, the base must be pink and the edging must be white. The exception to the stamp on the base is on Woody the baby and some Annabells. The first batch of pigs that were made for Natwest were by Sunshine Ceramics. These pigs will not have an embossed marking on the base. Only 400 complete sets were made by Sunshine Ceramics, but 100,000 woodys were made. The production was taken over in 1983 by Wade. All pigs made thereafter have Wade England Emobossed. There were some Annabell pigs produced with Made In England Embossed on the bottom but it is not known who made them.
Another thing I have noticed on the base of some of the fake pigs is the ring around the hole. The hole should be perfectly round but the indented ring around it should be almost egg shaped. I found a picture on ebay where the indent was round. If there is anything about a pig that you are unsure of then DO NOT bid for it, even if it is a very good price.
Most people will have heard about the White Sir Nathaniel, who is reported to be worth a fair sum. Unfortunately Wade deny all existence of these and they are certainly not part of the Natwest promotion. These are to be avoided as they are fakes.
There were also gold woodys produced by Wade, again these should have Wade England Embossed and these must have the Certificate of Authenticity with it. A very limited number were produced and 25 were given away a prizes on a Tresure Hunt competition run by the piggy press. No other pig was ever produced in gold except one Sir Nathaniel in a gold suit with a blue spotted bow tie. But as only 1 was produced you can be sure if any show up they will be fake.
So to simplify all this. There are 7 genuine pigs - Woody, Annabel, Maxwell, Lady Hilary, Sir Nathaniel, cousin Wesley and Gold Woody. The base of all should have Wade England embossed except a few Annabels who may have Made In England and some pre wade woodys who will have nothing. All but the Gold woody should have a pink base with white edging. Get clear pictures of the pig but mostly the base to check the marking on the bottom.
And most of all if you are unsure for any reason, DO NOT BID.
I hope this information helps, and hopefully will prevent people buying a fake pig.