Misfiring again, full tune-up?!

[zoldos]

It was misfiring on cylinder 5 some time ago. A new spark plug, coil, and injector cleaning fixed it. It ran like a race horse for months and months. Now it's misfiring on cylinder 3. The mechanic I use said he'll do a full tune-up this time, all new spark plugs, plus a new coil for number 3. And the usual other stuff.

Is this good? Do I need all the coils replaced?

I don't know anything about vehicles. lol

Thanks!