I've been after a Constellation for months. The first one was dirty and dodgy. It went back. The second was beautiful but Omega service UK had replaced all the bits that gave it an identity and then failed to document the changes, leaving it with the wrong calibre number and no provenance. Not what you expect from an ISO registered company. It, too, went back.
The third had "never been molested nor opened" but the the case had been filled with soft solder where somebody had tried to saw it in two! It didn't stay.
I had been looking for a C case with a 550 series movement then this came up in Orlando with a box and a full set of papers so I settled for a 751 movement and an integrated bracelet. On arrival, slipping under the customs radar, despite being honestly described, I opened the back to confirm that the certificate of high performance and the guarantee did, indeed, match the serial number and found a recent service mark and a newly fitted gasket. It ran 295 degrees and +1s/d on the machine and I absolutely love it. This one will not be going back!
Big thanks to Dr. Frankenstein's nemesis, Desmond, for the imparting of his knowledge and confirming that it was authentic.