In many professions, finding two helpers for the same job was avoided as it would make the other party feel that they were untrustworthy.
However, it was different when it came to the appreciation and authentication of artwork. Normally, a piece of valuable artwork required more than three official authentication organizations to authenticate the artwork.
This was in part due to the buyers. As there were so many buyers all over the world, they could not possibly all trust a single authentication organization. Some would trust one organization and others would trust another. So, in order to sell for a good price, it was best to get both organizations to carry out the authentication.