The participant has no way to decide between the two packages or know which one is the placebo and which one is the real thing so he doesn't need to go through the process of flipping a real coin.

I am worried that standardized shipping will come with standardized package layout, and I'm guessing "preference of left vs right identical thing" correlates with something the system will eventually test. Having thought about it more, this is the real issue with allowing customers to choose which product they'll use: that decision has to be purely random if you want the math to be simple / understandable. I agree people are unlikely to actually flip a coin :/

Thankfully the fix is easy: you have the testing webapp decide for the participant. They receive the product, enter the numbers online, and are told which to use.

For non-crossover trials I agree this needlessly increases the cost. It's almost surely better to use a trusted third party.

That means the participants has to do the work of going to the post office and remailing packages. Some of them will require additional time to remail and it might produce complications.

Agree. I think having a trusted third party handle the shipments is cleaner at the moment. I'm still curious what blogospheroid's thread comes to. It seems like the paranoia of cryptoland is helping us see some more holes in modern experiment design (ie your thread on poisonous placebos).

Maybe you can win a company such as Amazon as a partner for distribution. Amazon warehouses can store both products and placebos and ship randomly.

Thanks for saying this. Looking closer, I actually think their existing Fulfillment APIs would just work for this (ie the webapp controls an Amazon fulfillment account, the person seeking a test ships two pallets of physical product there, the webapp says where to send them).