There is a lot of difference between offering a garland of flowers bought from a shop and one that we make out of flowers picked from our home garden. When we plant the flowers, water them, pick the flowers, make the garland and take it to the temple, thoughts of God alone live in our minds. The Lord accepts anything offered to Him with intense Love. When we buy a garland at a store and place it on the deity it is only a ceremonial act while the other is a garland of pure devotion and an act of love.