Matthew and Hi-Man showed up on time and were very patient when I described the problem to them. My house has a leaking issue in the garage from the decking upstairs. In the very beginning, Matthew thinks it is drains' issue, but after listening to my concern, Matthew agreed to perform some experiment by pouring waters on the drains. They did it over and over again with patient and Matthew inspected the problem with cautious.
At the end, Matthew concluded it should be a deck issue but not drain issue. They clean up everything and swept the floor before leave. Very professional. Although there is $79 charge, for the time and inspection they had done for us, it's worth it.
Comparing with the other plumbing company who said they will fix the drain/pipe issue for $1,750 and could be more if they find the root cause, Thousand Oaks Plumbing is a more trustable company because their employees are well-trained and they are very honest by saying this is not plumbing problem but deck issue.
Thanks again to Matthew, Hi-Man and Thousand Oaks Plumbing.