I'd have the pen fixed up into working condition and use it with the replacement nib, that's the simplest way out. You could, I suppose, sell the pen "as is" with the nib it has to finance the purchase of another pen that's correct. Did the eBay listing have any information about the condition of the pen? Even the dullest of sellers should be able to read the words on a nib. Best of luck. Keep searching and if you live near London, in the Autumn there's a pen show I believe. Always a good spot to get a working Vac. from a reliable source.
Edit: Another thought, Henry might have a suitable nib, could a swap be arranged? Your nib + cash for a Vac one?
I know that using the pen with the replacement nib is the easiest way out, but I'd much prefer to have a nice Vacumatic with a genuine Parker nib. It may not write that much better than the nib I've got and cost me a whole load of time/money, but it's a "peace of mind" type thing, where I'd be a lot more satisfied with the "real deal" so to speak. The seller did state that the pen was in "good working order" or similar which I've found to be a blatant lie, so maybe I could pursue a return/refund and start over.
The London pen show is definitely on my radar, I'll be visiting if I am free on the day.
I will also discuss with Henry the possibility of swapping/replacing the nib.
Can it be returned because not as advertised?
This has definitely crossed my mind, I may send the seller a message once I've had a play around with the mechanism. I fiddled with it a little and managed to get the button to depress fully but it doesn't appear to be sucking up any ink as such, although I haven't had a chance to properly try to fill the pen.
I would return the pen via ebay's Buyer Protection program...By the time you buy a new nib and have it repaired, you would probably have a hard time even breaking even...Besides, there are plenty of Vacs out there and you should have one that you are happy with.
This sounds like a good idea, I'd like to have a fully working Vacumatic that has the original nib rather than settle for "second best". I'll look into getting a return/refund.