I guess they might not know that your house is tidy and clean and without actually viewing the actual unit, they are also taking a risk on what needs to be done.
HAve you gotten them to come down and take a look personally? If your place is so tidy, you might be able to nego a much better rate.
I have previously used this firm Clean and Fix.
www.cleanandfix.sg. Was happy with their quote as it wasn't too high and their folks were on time and did the job. Y