No, you won't need any of the base station's passwords from the seller. You can perform either a "hard" or "factory default" reset on the Express and this will delete any passwords that are set from the previous owner.
Perform a Factory Default Reset on the Express as follows to get the device back to new, out of the box settings.
Power off the Express
Wait a few minutes
Hold in the reset button first and continue to hold it in for an additional 9-10 seconds while you simultaneously plug the power back in to the Express
Release the reset button after the hold period and allow a full minute for the Express to restart to a slow, blinking amber light
The Express is now reset
If you are asked for a password, the default is "public" (without the quotes)