It is better to give such a reply to the greeter -

بَارَكَ اللَّهُ لَكَ وَبَارَكَ عَلَيْكَ وَجَزَاكَ اللَّهُ خَيْرًا وَرَزَقَكَ اللَّهُ مِثْلَهُ وَأَجْزَلَ اللَّهُ ثَوَابَكَ

Baarakallahu laka wa baaraka 'alayka, wa jazaakAllahu khayran, wa razaqakAllahu mithlahu, wa 'ajzalallahu thawaabaka

May Allah bless you, and shower His blessings upon you, and may Allah reward you well and bestow upon you its like and reward you abundantly.

Reference: This is what Imam Nawabi in his Al-Azkar text p. 256/349 mentioned