So I had my Steam game installed in H:\Games and wanted to move it to C:\Program Files (x86)\Steam\steamapps\common\.
I followed this Steam guide on how to move a Steam installation. I moved my game folder to a safe location while steam was closed. Then launched steam, right-clicked the game in the library, and deleted local content. I closed steam again, moved the backup game folder to my target location in the common folder. I opened steam and found the game greyed out as if it was not installed. I entered properties and could not verify the game cache. It prompted me to install. I installed it to the common folder and it was downloading. I tried to vertify it, but it did not vertify, just kept downloading.
The game is Borderlands 2.
preparing to installdialog closes, you should seeDiscovering existing files. If you do not see this message and Steam starts downloading the game, then the existing game files are not in the right location. The existing files need to be in the exact same place as where Steam tries to install the game. I cannot post example screenshots right now. – Oct 19 '15 at 08:54