One of the great advantages of the MPLS VPN architecture is that VPNs can be merged easily between different customers' intranets to create specific extranet VPNs. You can create an extranet by importing and exporting routes between different customer VRFs.
If IP address overlap between customers is not an issue (that is, the IP address space is unique between customers), then you can import routes directly between the VRF tables.
After an extranet is created between different VPNs, the customer intranets are subject to access by hosts outside their own VPNs (from the extranet). Although the intention to allow an extranet might have bona fide business reasons (for example, to allow ordering between supplier and manufacturer), ...