1945 New Zealand Halfcrown

It must be remembered that a dealer in order to make a coin attract a prospective buyer will offer the coin at below catalog value.
He has to make a profit at below catalog value ($225), so he will buy it as stock at perhaps 50% to 75% of his sale price.
That may work out at maybe $100 to $120 for the dealer to buy it as stock, considering the value reduction caused by the spot.

If your grading is correct. and it appears to be, then
$50 is quite OK for the price you paid.
The spot will affect the value a bit, but is sufficiently small enough for the value reduction to also be small.


I bought a 1934 Halfcrown in good VF (condition nearly, but not quite as nice as yours), and I paid AU$3 for it, but that was a long time ago. (20years?) It came from a dealer's junk box.

I'd happily pay $50 and remove the spot.

Nice AU-58. Anything you do to try to remove the spot might make things worse. It has nice eye appeal as is.