Is there an appropriate phrase when some-one says 'sadhu' to you, for example after making an offering at a monastery? Saying 'no worries', or 'that's okay' doesn't seem appropriate. Is there a appropriate response, or should I just smile and accept the compliment?
**“Namo Buddhaya!”**is what is most appropriate IMO. Ven. Gnanananda Thero of the Mahamevnawa in the year 2011 requested from devotees to say 'Namo Buddhaya' whenever we meet or depart, and this is his reasoning for getting us to do so:
”At the time when the Supreme Buddha was alive, it was the practice observed by His disciples to place both hands together in a gesture of worship and greet each other by saying ‘Namo Buddhaya’, whenever they met. Owing to the influence of this ancient Buddhist practice, today, whenever Hindus meet one-another, they too bring their hands together and say ‘Namo Narayana’ or ‘Oh Namah Shivaya’. Some Buddhists too say ‘Namo Sairam’ when they enter the ashram of Sai Baba. But the words ‘Namo Buddhaya’ have been forgotten by the Buddhists. I realized that these old values must be rekindled. Accordingly, I made a request from devotees on this Sri Sambuddhatwa Jayanthi Vesak Full Moon Day that the greeting ‘Namo Buddhaya’ should be brought back into usage once again. This is a noble phrase that had been in use in our country for several centuries earlier. ‘Namo Buddhaya’ connotes that; ‘May this Salutation be to the Supreme Buddha’. The four-fold disciples, who have recognized the three refuges, use the phrase ‘Namo Buddhaya’ quite happily today.”
If someone says "Sadhu!", then you too can reciprocate by saying "Sadhu!" or "Namo Buddhaya". We say ‘Sadhu’ to show our appreciation of something. We as disciples of the Supreme Buddha say sadhu three times to express our happiness or approval of something related to the Dhamma. Now a person may ask as to why we should keep our gathered palms near chest or forehead or above the head when we say “Sadhu Sadhu Sadhu?”, Why three times and not four times or two times? My answer to such questions of course is not to dwell in such irrelevant questions, as then it is stretching this a bit much.