Was this a vendor with some history on Gunbroker? If no significant sales history, some other form of personal references would be appropriate. Otherwise what you asked for is certainly reasonable. If you wanted other "proof", you could always send a FOIA request to the BATFE on that serial number to see who really owns it, or if it even registered. That takes a lot of time though. I'd give the vendor a week to send the info electronically and if no action on their part is taken, contact Gunbroker to report this as a problem vendor. When I sell, I file e-forms and I don't even accept payment until the e-form is approved, but I don't ship until I receive full payment. The buyer can check e-form transfer approval on their e-form site independently so there's virtually no way to defraud on either side. Some owners don't know how to use the e-file system, aren't SOT holders, etc. Working deals with those vendor/owners is just riskier without bonafides of some sort.