When we meet a person in the morning we say 'Ohayougozaimasu.' but you meet the same person again in the day, we say 'Otsukaresamadesu' rather than 'Konnichiwa.'(=Hello). 'Otsukaresamadesu' means 'We appreciate your work' if I simply translate. This is very common and usefull. You can say to business partners whose postion is lower position than you example for subcontractors. Never say to your important and bing accounts.