Your electric bill and your comfort will be the worst of and issues as with the fan pulling air into the unit heat from the living space will not dissipate out. Air needs to be sucked from the outside in of a condenser ( heat pump) and dissipated into the air out on top so in one case your neighbor is right, air should be blowing from the top upwards and hard. With the air pulling in you will not be cooling your home as the heat that is supposed to be extracted from your home will just re-enter you refrigerant cycle and never really go anywhere so your system could run a long time and do nothing. Is this the case?
Polarity needs to be switched if it truely is running backwards meaning two wires are hooked up wrong, reversed. Your neighbor should have switched polarity around and got you going instead of just trying to sell you new equipment. I've seen motors run backwards for months and never have a problem once switched back as they can run in either direction for the most part so applying electricity to it won't damage it in either direction so new motor is iffy at this point, IMO. Yours is still running years after the fact so it's apparently still good, just reversed.
Some neighbor you have.