None. Once in the last EU, there are no restrictions on movement between EU states. The same is the case for Annex A species. I see that you are referring to Appendix II - you need to check the EU regulations, which use Annexes. Some App II (which would be Annex B) are elevated to Annex A so require valid A10 certificates to be sold or bought. For example, Javelin sand boas are an Annex B species throughout the world, but in the EU are in Annex A, the same as Appendix I species.
Provided the animals are either CB or were lawfully imported then you don't need any other paperwork. Don't forget that all boa and python species, apart from a tiny number which are Annex A, are all Annex B, and no documents are needed.
If you want peace of mind, ask for a receipt with the seller's details, confirming that it's captive bred.