In Australia there are extremely strict "false advertising" laws just like you propose.
A few years back Holden (GM) had an "Employee prices for all" sale - so supposedly regular people were getting the same deal that employees were getting.
It came out a while later that wasn't true, and so Holden (GM) were forced to give customers a refund of the difference to the tune of hundreds of millions of dollars.
If you advertise it, and it's not true, you'll be forced to make it true.