no way, how does the "clear flat finish" stick to the oil?

you need to lightly sand it just to break the gloss of the oil, and or, apply a quality bonding primer and then QUALITY top coats

Thank you, christophern! It didn't sound right to me
either.

That painter isn't a painter. From his knowledge about sanding, I'm going to guess he's never sanded anything in his life.

All you need to do is lightly sand the oil paint just to rough it up so it will take the primer. Then you prime with an OIL based primer. I know this doesn't seem to make sense but this is what my paint store guy told me last week. Then you paint over that primer with latex. I use Benjamin Moore paint. I have the same problem. Oil painted trim throughout my house done 20 years ago which I now have to change. I'm in Canada and oil based paint has become illegal here for environmental reasons for the last couple of years.

OIl based primer would certainly work but is hardly necessary.

If oil based is illegal in Canada, then how can you recommend priming with an oil based primer? Personally, I think a high quality acrylic primer is actually superior to the oil based primers for bonding purposes.