That's not strictly true. Even if there's a receipt in the box saying something is worth less than US$200, if the customs people think it's worth more, they can decide what they think it should be worth and tax you accordingly. But if you buy something on eBay, you should be able to argue the point - via Aeropaq - that that was it's market value as you bought it online. The shippers all have good relationships with the aduanas, so it shouldn't be a problem.