I have seen bikes come out of boxes that are a hot mess. The LBS I go to does offer assembly like the one the OP mentioned. I have seen frames warped, BB's that are like the Sahara desert, wheels that were barely tensioned, grease where it shouldn't be, no grease where it should be, etc. Why not let an expert take a look, torque things down properly, use their skill to assemble a bike that you will be putting your life at risk on.