The trouble with painted location walls is they're usually aged already. I matched the colour and sheen, (my first hint: it was almost impossible to match) but the patches showed after the painters patched the walls. The wall aging and fading varied throughout the room, and it was impossible to get a true match.
There's no way out if a location owner isn't happy with the patch jobs. Often, after a shoot the painters need to fill the goudges the grips left in the wall (its always the grips). Sometimes, though the whole room doesn't need a repaint if the patches diddn't work out too well. A tip from a seasoned painter was just to paint the damaged walls. But I had to paint out the whole wall, or if there was a jog, just to the jog. Corner to corner.
Because of the way light plays on the walls, it works like magic. The eye doesn't pick up the subtle colour shift at a change in the wall angle.
Another tip was to muddy up a bit of the paint a little with a teeny tiny dab of diluted raw umber. It's the magic scenic dirt tint. Kills the hotness of a brand new colour. Seriously, its quicker to just paint the damn wall.