Can't tell from here. Does he have any crack smoking symptoms?
Yes, computer swapping is not too difficult. If you can induce someone to pay you $1200 to change their computer, would you do it? IOW, do you have a conscience?
Any way, you can order from the parts stores, or actually find out what's wrong as an alternative.
TPS code and a P0302 misfire on #2 would be handled separate from replacing the computer. TPS - you can clean them, as all they are is a 'volume control' that tells the computer how open the throttle plate is. Misfire can be spark, fuel, or mechanicals. Spark would be the plug, wires, boot or COP or coil, depending on vintage / engine.
Fuel would be pump, filter, fuel line, regulator or injector, computer running those a the last spot in the list generally.
Mechanical would be the induction system, MAF, ribbed air tube, throttle, intake manifold, valves, pistons, rings. Computer involved in reading what the MAF sends.
I would pull spark plug & wires for #2(passenger side plugs). How old are the plugs? The wires? Do you see a 'light show' if you open the hood with the engine idling after sunset?(dark thirty) Plug wires can degrade and cause misfire. Again, computers far down the list.
Or, just give the guy your money and make sure he agrees, 100%, that if this does not fix it, you get your money back, 100%, no questions asked. If he agrees to that, ... well it's up to you. I bet a nickel he will not. (cuz he's likely a 'parts changer', and could not analyze a problem and reach a conclusion and propose a solution to save $1200 if it was his own vehicle)
tom