Just as an fyi, it sounds like they may have fixed your slipping seatpost, but mine had the same problem (was working with a fitter - I kept complaining the seat was to low, he would raise it, I would come back complaining it was to low...). It needed carbon paste put on the seatpost, then it hasn't slipped since (why didn't it come with carbon paste already on there?? I have no idea). My intent in saying this is just to let you know in case you have further problems with the seatpost slipping.