I have found that the more demanding the agency is about you sending them payment upfront, the less likely their donors were verified in any way. I found Peas in a Pod and Northeast Assisted Fertility neither demanded any fees until you were ready to sign contracts with their donor, and they were upfront about what info was verified (ie they have seen the docs and were willing to send them to my nurse for confirmation). With Peas, we also have had the donor's records sent and reviewed by our RE for no fee.
The other agencies I contacted all wanted money before anything. And those that didn't simply did not call me back when I shared that we required verification of stated data.
Once you send that money, you will not be getting it back, so be careful...your chosen donor may not work out with your RE, she may cancel on you...good luck getting any money back from agencies that needed a "deposit" upfront to do their job.