WWE announced that WrestleMania 37 nights one and two were attended by a total of 51,350 fans with both nights selling out.
Each night had 25,675 tickets sold according to WWE and if that is an inflated number, it was not overly inflated as in previous years for obvious reasons.
Weeks before tickets went on sale, there were rumors that up to 45,000 tickets were going to be put on sale for each night but a more sensible decision was taken by changing that to just 25,000.
With no international fans, it would have been extremely hard to sell 45,000 tickets each night and tickets only went on sale three weeks before the show.
Ticketmaster only had a few hundred tickets remaining on sale before each night so it is completely possible of a legit sell-out.