Find another archery shop then!!
A well tuned bow, no matter how old, will certainly help your situation. However you may still have that odd arrow/broadhead combination. First thing you should probably do with the arrow/head that doesn't fly the same is roll it on the corner of a table to see if there is any wobble on the tip of the b-head. Over the years I found that this was more the cause than misaligned vanes.