after last service with Lexus can not trust them anymore

Hi There, I took last year my car to Lexus Fourways and they took my car for regular service then they came back and told me that your water pump is leaking need to change, then I did not trust them, I just want to see water pump is leaking or not, Kennith took me to show the problem and I touch the water pump and it looks like a wet. so I asked them not to change it, now after year still my water pump is ok and not leaking! so my next service coming and how can I trust Lexus not lying to me ?