Did they replace only 1 plug and coil? If so go ahead and replace them all. Proper gap on the plugs is important as well.

And since you are already replacing things, replace your mechanics for known good ones!

 

Before you throw more $$$ at that shop get a 2nd opinion from a known reputable indept mechanic.

Maybe you can take the shop to small claims court when you find out that the "repairs" they performed were not necessary.