LEGO is one of the most reliable things to resell, but value varies hugely. A sealed retired set can sell for many times its shop price, while a tub of mixed common bricks is sold by weight.
Sealed and retired sets
Sets that are no longer sold in shops ("retired") and still sealed are what collectors want most. Check the box for damage, crushed corners and broken seals, because condition matters a lot to collectors. The set number is printed on the box and helps you identify the exact set.
Complete used sets
A used set is worth much more if it is complete, with instructions, and better still with the box. Themes such as Star Wars, Harry Potter, Technic, Creator Expert and modular buildings, and older castle, space and pirate sets, are popular. Online catalogues let you look up a set by number to check its parts and minifigures.
Minifigures
Some minifigures are worth more than the sets they came in, especially rare characters, exclusive or promotional figures, and older figures in good condition. Collectible Minifigure series figures sell individually. Check for cracks, faded prints and fake parts (non-LEGO figures often have a slightly different finish and no LEGO stamp on the studs).
Loose and mixed LEGO
- Check it's genuine: real LEGO has "LEGO" on each stud. Mixed tubs often contain other brands.
- Pull out minifigures, instruction books and special pieces before selling the rest.
- Bulk LEGO is usually sold by the kilo. Clean, sorted and genuine bricks sell for more.
Things to avoid
- Badly yellowed or sun-faded white and grey bricks.
- Sets described as "complete" that you can't check.
- Smoke-damaged or very dirty bricks, unless you're prepared to clean them.
Pricing
Compare against the same set in the same state (sealed, complete with box, complete without box, incomplete), and check eBay's Sold items filter to see what similar lots actually went for. Say exactly what's included in your listing and photograph the minifigures.