Hi A B,
Unless the seller explicitly also sold you his VMware Fusion 6 license then I'm afraid there's not much we can do to help you.
Left installed by the previous owner doesn't make the software your property.
There's the following statements in the VMware EULA (from Fusion 7 in this case as it is the most recent)
Emphasis is mine.
2. LICENSE GRANT.
2.1 General License Grant. VMware grants to You a non-exclusive, non-transferable (except as set forth in Section 12.1 (Transfers; Assignment) license to use the Software and the Documentation during the period of the license and within the Territory, solely for Your internal business operations, and subject to the provisions of the Product Guide.
and:
12.1 Transfers; Assignment. Except to the extent transfer may not legally be restricted or as permitted by VMware’s transfer and assignment policies, in all cases following the process set forth at www.vmware.com/support/policies/licensingpolicies.html, You will not assign this EULA, any Order, or any right or obligation herein or delegate any performance without VMware’s prior written consent, which consent will not be unreasonably withheld. Any other attempted assignment or transfer by You will be void. VMware may use its Affiliates or other sufficiently qualified subcontractors to provide services to You, provided that VMware remains responsible to You for the performance of the services.
In case of doubt you can always contact VMware Sales.
But in no circumstance can anybody here in the forum help you as your copy being correctly licensed is unclear and the Community Terms of Use explicitly forbids helping anybody here with piracy.
Hope this helps,
--
Wil