Flushing The Cooling System.. Is it really Necessary every 25k

Your owner’s manual will tell you.

There is no standard that covers all cars. Designs vary. Coolant varies.

I can tell you that it is very cheap insurance. Pay a little bit now or a whole lot more later.

Follow the manufacturer’s recommended maintenance schedule. Not following it is one of those penny-wise, pound foolish sorts of things. Allowing other people (like auto shops) to tell you what to do is a good way to get taken every time you have your oil changed.