I personally will turn down a note that has been pressed and washed, and especially one that smells of the process. I will contradict myself now. Yes I have purchased notes that have been processed, but the only time I have picked up processed notes, is of one that is very tough to obtain in any condition. I am not sure who the dealer is, but if the condition of the note is truly bothering you and you feel the note was misrepresented, then I would contact the dealer to express my thoughts concerning the note. If he is a reputable dealer, then I am sure he will stand behind what was sold and will offer a refund. On the other hand, if you paid a ridiculously low price for the note, it might be worth holding on to.
So in short, a pressed is not as marketable as an original note. Yes the grading will be affected. If the note is ever graded by a third party, there is a chance that it will be noted on the holder. Thus it will most likely affect the price of the note.
Just my thoughts