I purchased a MacBook and it has the previous owner iCloud locked how can I remove this?

If the device is Activation Locked, that suggests not only that the owner did not prepare it for resale, but that the owner marked the machine as Lost. Why would they do that? Because they considered it to be lost or stolen.

You bought a brick, which should probably be turned over to the lost & found department of the local police.

See also the discussion in:

MacBook Pro - Apple Community

Most likely stolen. I wouldn't think the pawn shop would want to be associated with selling stolen merchandise. If they will not give you a refund, you may want to escalate the matter with them including online reviews letting other people know of the practices of this business.

As stated already, the Mac will never be usable without the original owners credentials.

Take it back to the seller. If that's an individual, it gets a little more complicated.