If the purchase was in cash for a second hand item (possibly third hand or more) then it becomes very dificult to track the buyer down. Look around a second hand store for a laptop that is more than a few years old and it is likely to have had at least one other owner since the original purchase. Do not use the laptop for at least 1 week, that way any CCTV from the store has been overwritten and really by the time they manage to trace it from the manufacturer through any owners and on to the second hand store it will be perhaps 2 weeks after purchase. At this stage even public CCTV records will start to be overwritten. If you bought one well in advance, i.e. 2 or even 3 months before you used it then it would make it nigh on impossible to find the buyer.

As an added level of security, a month after buying it make a post on craigslist to sell it as broken/not working. send an email to yourself from an internet cafe offering to buy it. Via email arrange a trade at a location without any CCTV. Plausible deniability if the police do ever show up at your door.