basicly there is no "real" way of knowing, what ash said...also you shouldnt be able to move the compressor turbine to the extent where it acculty scrapes the housing. Dont spin the turbo with an air compressor!
LOL YES YES YES Do Not use an air compessor to bench test the turbo, it will mess it up. Look at the side walls and see if the blades have been scraping the housing on it. It should move freely and smoothly as you turn it by hand. Clean it up good and look into braided steel lines for the feed and return.
also, sorry kiddi but i wouldnt recomend a braided return, not after (i believe it was) 40bob said on Turboford....caused the turbo to go bad. If you do recomend and go with a braided return, make sure it is AS big if no Bigger than the stock one.