It really depends. There's no one right answer. If you're an experienced seller on eBay or Craigslist, you will likely get the highest value for your Surface laptop on those platforms. However, they do require more effort from the seller, charge fees, and come with risk of fraud that novice sellers may not know how to protect themselves from.
If you share some of these concerns, we recommend using a trade-in site such as ItsWorthMore. Trade-in websites leverage their volume discounts and industry know-how to provide a smooth streamlined experience; for a slightly lower payout.
Another alternative is to trade-in your Surface laptop directly with your big-box retailers or with Microsoft. These typically offer the lowest payouts.
Some non-functional Surface laptops do not have much of a resale value and you can choose to recycle them. Recycling in an environmentally friendly manner helps keep toxic pollutants, such as lead, out of the environment. Keeping us all healthier and happier!