No. And I'm not sure that any of these companies CAN employ under 16's directly. At this time many companies ask on the registration forms if shoppers have children because there are 'child friendly' and 'child required' shopping jobs. This is why I was suggesting you work with/through a parent to perform some jobs.
And yes, the payment would come to your parent, in your parent's name and be taxable to them. So you need to talk with them about what it is that you want to do and see what you can work out with them.
I suspect that you are comfortable with the internet and with forums but your parents may not be. If you need someone to answer their questions about you mystery shopping, have them use your log-in to send me a Personal Message (just click on my name and you will get a screen that allows you to send a personal message).