People hate the phrase for a couple of reasons. One is that it feels presumptuous. The writer presumes that you will provide what is requested and so is “thanking you in advance.” Would the proper response be “You are welcome in advance”? That silly suggestion shows how “Thank you in advance” comes across wrong.
“Thank you in advance” also suggests that the reader will not be thanked later on, after fulfilling the request. If the reader receives thanks in advance, will his or her actions be thoughtlessly ignored?
Source: businesswritingblog.com
