How to unlock the Garmin c550?

I have the same unit and the owner's manual gives you only two options. You can either use the PIN number or drive to "The secured location". This is something that you set. The owner could simply drive to a secret location that they set and the unit would unlock. The manual states that you must send the unit to Garmin to have it unlocked if you forget the PIN and the location. I would keep trying to contact the seller. Otherwise you'll have to send it to Garmin.

With no response from the seller, my guess is that the item was stolen, only way to unlock it as the prior post states is to send to Garmin if the unlock code/location are not known. If it is registered, it will be unlocked for the registered user.

Garmin Lock

I would have to agree with weebl.

Keep trying the seller, and perhaps call Garmin, tell them how you bought it and give them the serial number.

I'd like to know how it all turns out. Keep us posted.