@Jaobler Do you mean this coin?
If you register for a free Heritage
account you can view prices realized from previous auctions; it's a great resource for learning the actual sale prices for specific coins.
I don't think the example you linked is obviously overgraded. Keep in mind there is a lot of variation between coins at a given grade. Your coin appears to be nicer than the NGC
coin but that's no guarantee it would grade higher.
I have no information regarding the relationship between HA and NGC
does offer a service for sellers to get raw coins graded for placement in auctions. I think a seller can specify which grading service they want in that case.