How can I tell if a wall and trim has been previously painted with latex or oil based paint ?

I need to possibly repaint in a house that is not mine, and will need to know what is there now so I can use the right paint to cover it, and to be able to do the proper prep work.How can I tell if a wall and trim has been previously painted with latex or oil based paint ?
Denatured alcohal, wipe your trim with it, if some comes off onto your rag it is latex, oil wont rub off like the latex will. keep in mind you can paint oil over latex but not latex over oil. The other guy has it backwards.How can I tell if a wall and trim has been previously painted with latex or oil based paint ?
Actually, you can use latex over oil providing you use the proper primer . I've also done re-paints where we have used 100% acrylic latex over oil and the adhesion is great .
Using masking tape, tape a very wet rag onto the wall or surface----wait an hour, and see if the paint under the rag has peeled or bubbled. If it has, it's probably latex paint, and should not be covered by oil-based paint.