Totally agree.
If there is an external component to this system, it is subject to being hacked. Nothing is out of the reach of a driven hacker if it is accessable.
The only way to truly make it hacker proof is to:
Make it a part of the person.
Make it dependent on the living, functioning person for operation.
Control access to the device itself, so a hacker can't get raw copies to play with.
A chip should be tiny. It should be programmable inside the person (insert a blank so the body is providing power, then upload the ID number.) The programming should be dependent upon the body for the power to maintain the programming (loses all data if the contact with a living body is lost.) It should be able to have the programming input mechanism destroyed after initial programming (like a PROM in a computer--destroy the input path, so no changes can be made.) It should only contain an encrypted ID number--no actual personal data (that should be kept on an external network.) It should be placed in the hand (ease of "swiping" across a scanner), or in the head (for those that have no hands/arms.)
Anything less, and the system becomes a hacking target.
With these safeguards in place, only the person is hackable ("Buy me a fruit pie, or I'll shoot you" kinds of stuff.) But, since the person would need to access a point of sale device, or an ATM-type of terminal, I doubt even armed robery by coercion would be possible (too much observation taking place.)
A system like this would, from a worldly view, be the absolute end all of security. And, it would be the ultimate in tracking ("No, officer, I wasn't at their house. Check my chip track, and you'll see I was at the library.") To those without the chip, it simply means you won't be able to buy or sell anything. Even barter could be stopped with careful tracking of people involved and the items exchanged. After all, a diamond ring moves from person "A" to person "B", that might well be a gift. But, a bag of groceries does the same thing, that would not likely be a gift, but a black market deal. Send in the "proactive" law enforcement to grab all involved, and sort out the specifics later.