Compliance teams love documents, so ask for them. InterLIR Global states that it does full KYC on every counterparty, complies with EU law and uses escrow for purchase transactions, and that it is registered with RIPE NCC, ARIN, APNIC, LACNIC and AFRINIC. Those are claims, so request their KYC process and a sample escrow agreement. For a regulated firm I'd also verify the broker in the RIPE registry. Buying
IPv4 properly takes paperwork, and that's normal. Ask for their sample contract, because auditors will ask where the money goes and which entity you're dealing with. Keep copies of the KYC exchange for your files.