Never end your email with “Thanks in advance”
Writing “Thank you in advance” in a letter with a request may be perceived by your addressee as an insult. More precisely, a person may consider that:
1) he is ordered to do something. In other words, the person has not yet agreed to do something, he is already thanked, forcing to comply with this gratitude. The applicant is sure that his request will be fulfilled and it does not matter to him whether the performer wants it or not.
2) after doing it, they are not going to thank him (after all, they have already said thanks in advance).