Woodworkers unable to remove stubborn stains from finished wood surfaces

Woodworkers and furniture owners struggle to remove difficult stains (water marks, discoloration, etching) from wood without damaging the finish or the wood itself. Current solutions either don't work effectively, require extensive sanding/refinishing that destroys the original finish, or involve trial-and-error with multiple products. This is painful because stained wood pieces lose value and aesthetic appeal, and professional refinishing is expensive.