Mutillids are about 4,300 species worldwide, with 594 represented on iNaturalist. The top 4 observed species on iNat make up 31% of observations and they are “common eastern velvet ant” plus 3 large, red-hairy species. Fifth on the list is a large, white-haired species.
Pompilids are about 5,000 species worldwide and so many similar species. I usually leave Pepsis at genus unless it’s a very obvious species like mildei. #1 for most observed spider wasp is Pepsis thisbe and I wonder how many are misidentified (P grossa is actually NM’s state insect!) or photo quality that isn’t enough evidence. Here’s a snapshot of common confusions.
For parasitic wasps, most people need to be content with “as good as it can be” at levels above species. Even well-marked Ichneumonids like Lanugo have look-alikes (Comsocrytpus) and may also mimic Pompilids or Vespids. In addition, they are mostly small and don’t often sit still.