1/2 New Penny 1971 Price Discrepancy

Not a fraud. A seller can ask whatever he wants up to $2500.00 on ebay for a raw coin.
Just because he asks an absurd amount, it doesn't mean that's what he will get,
they are just preying on the uninformed hoping someone will pay the price.
If you want to see what coins are really selling for, see what the coins have been sold for,
this gives a more accurate value.

Yes, high asking prices, not selling prices. For some unknown reason people appear to think 1971 decimals are rare and valuable though then fail to ask themselves why they and all the others offering them for sale have so easily found so many. If they'd bothered to spend 60 seconds on Google before listing they would know 1971 is the most plentiful decimal date, the numbers minted being in the billions.
As JimmyD points out, you can ask whatever you like for anything, it doesn't follow someone will pay it.
In front of me as I type this I have a black pen which still works but is missing the cap. Yours for £1,000.
No?
See what I mean?

I'd be very surprised if any money actually changed hands.

Weird auctions like that can be a simple way of money laundering, some overseas buyer buys something worthless then "pays for it" - thus transferring the money from abroad.. for a legitimate reason.

Yes. Any time you see a cheap coin - like a 1971 halfpenny or a 1965 American cent - offered for thousands of dollars, with no explanation for why it might be valuable other than "it's rare", it's almost always because of money laundering. Criminal A "sells" a coin to Criminal B for $20,000. Criminal B then sells a coin back to Criminal A for $20,000. Hey presto, Criminal A now has $20,000 of laundered money. Of course, with ebay, it's entirely possible for A and B to be one and the same person, with different accounts.

Of course, if innocent person C happened to wander into the scene and decide to pay Criminal A $20,000 for their "rare coin" instead, all the better. That way, both A and B get to keep the money. But money-laundering listings aren't really designed to encourage that happening.

Money probably did indeed "change hands" - it has to, for the laundering thing to work. But I doubt any actual coins were mailed anywhere.

It should be pointed out that offering to sell a "raw" coin (i.e. a coin not in a third-part-grader holder) at a price above US$2500 is against ebay policy. So if you see one of these listings, report it.

Website? Probably not a comprehensive one that'd cover decimal 1/2ps as they have very little value. Nobody is going to auction them in a genuine sale, which is where the reliable sites get their price data.

But something like the British Coins Market Values 2023 book, or Spink's Coins of England would cover those, and more? Though the 'price' would, like common stamps, be more related to how much a dealer would charge to list and post the thing to you than what it's actually 'worth'. If that makes sense?

This is Buy it Now on ebay currently