I have known several families who have done kidney donation within their family. Being a match and keeping their loved one off the list for donation.
Which got me thinking, should we be able to sell a kidney?
The average wait time for a kidney can be 3-5 years.
Its actually legal to sell body parts "for research" if you are a broker, assuming the parts are from a cadaver. This is likely used as a loophole to send transplant material over-seas where transplants can be performed. This is probably why the FBI raided MedCure.
And just in case you needed a reason not blindly to opt into tissue donation...
As for you question, I'm on the fence. I'm a libertarian sort of guy, but even I can see the potential for people being coerced into selling a kidney against their will. On the other hand, making it legal would end a very dangerous black market that takes more lives than it saves, and prices for an organ would drop dramatically.
If there was a mandatory 1 year waiting period between the decision and the actual sale, I think most of the drawbacks would be minimized.