Pretty much the testimony all over this forum of people having great experiences and results with them.
Check out the gratitude threads like this one:
This dies depend on you. It seem, or I notice, that those that approach any being from a place of feat doesn’t get the greatest experience. If you have any fear about then I’d say hold off and read around until you can stand toe to toe with them in all confidence.
There’s only 72 of them, they are called “Goetic” because that’s the grimoire they are in: the Ars Goetia. I like Corwin Hargrove’s book “Goetia Pathworking” as a very accessible way to contact them, and it lists all with what the author has experience of them providing for him, which I have found works out to be verified.