I don't know the concept of how iclickers work.
I am trying to buy iclickers cheap from people, but my worry is that if an iclicker is already registered with a person's name who I am trying to buy it off from, then would that have an issue with buying an used iclicker? If you know what I mean.

You can always re-register the used iclicker so it's totally ok to buy the used one )

Reregister it it should wipe the previous one. If you just bought it used, log onto site type in your info and barcode done