Highballing is the term I associate with that practice, although I haven't found much to support that use of the term. Wordnik quotes an example from The New York Times:
The only way Bush cut his “deficit in half” is by taking spending for the Iraq War and a whole bunch of other expenditures off the books, and highballing the predictions in the spring and then claiming he came in way under when his doomsday numbers didn’t come to pass at the end of the year.
Also, such estimates may be called inflated or puffed up.
Edit: Note that to highball is the opposite of to lowball, “to give an intentionally low estimate”, in some senses with intention to deceive and in others without. Regarding etymology of lowball, wiktionary says
American railroad term that described one of two positions of the ball of a ball signal. This is the same history for highball. ...
Also, as Jones points out in a comment, wikipedia suggests that the appropriate answer to the question is door-in-the-face technique. The wikipedia article says:
The door-in-the-face technique is a compliance method commonly studied in social psychology. The persuader attempts to convince the respondent to comply by making a large request that the respondent will most likely turn down; much like a metaphorical slamming of a door in the persuader's face. The respondent is then more likely to agree to a second, more reasonable request, compared to the same reasonable request made in isolation. The [door-in-the-face] technique can be contrasted with the foot-in-the-door technique...