You have to paper tune the bow. The guy at the shop might hold / grip the bow differently than you.
At any rate the bow must be retuned after installing a new string, in your hands.
I paper tuned my bow, using Blazers, Slick Trick standards fly same POI as field points out to 60 yards.
You did not say what head you are attempting to shoot; heads with more blade surface area are more challenging to tune.