Refinishing Correctly...

We always sand off prior varnishes and coatings
Because you just don't know what the previous
Owner cleaned the cabinetry with...Pine Sol,
Palmolive and Murphy's Oil Soap are commonly used
On varnished cabinetry and it has to be removed
As it contains animal fat triglycerides which
Prevent adhesion and proper bonding of cabinetry
Lacquer.

Anyone telling you they can refinish your cabinets
While still attached to the hardware is avoiding
Proper surface prep and required sanding.