Absolutely, definitely, check the rangefinder for focusing. Put on a fast, long lens, such as the 50 or 75mm summilux, or the 75 or 90mm summicron and do a focus test wide open at different distances to see if your rangefinder focuses well. If not, you can either exchange the camera immediately, or go through the adjustment yourself following the steps described in other posts on this forum. I tested my M8 in the store with a 50mm summilux because i didn't want to deal with any of these adjustments and because the demo camera I used backfocused. Be careful though which lens you use for testing. After doing the backfocus testwith a 50mm summilux, I ended up buying the aspherical version of this lens.
