I do hope that the rest of the machine is kept in finer fettle than that of the instrument panel condition...
With a potentially over-reading tacho or too fine a pitch prop on the front and it being flown in this condition without anyone seeming to care about your concerns make me think your money might be better spent at some other establishment.
Incidentally, all the C152 tachos I've seen/flow maintained have a green arc from 2000 - 2550 as the normal engine range of operation so the tacho fitted may be a 'non-genuine' one. Exactly what should infromation be displayed on the instrument panel, instruments and elsewhere on the airframe will be in the Placards section of the POH for that specifice aircraft (by registration/serial number not aircraft type).