How can I tell if a used version of Photoshop CS5 has been deactivated before I buy it?
I don't think you can, and buying an old copy of PS is extremely risky. It's nearly certain to be a fake.
You cannot until you try and activate it on your own computer. It's 99.99% likely to be cracked and/or come with malware or viruses.
Keep in mind that CS 1, 2, 3 & 4 are now dead versions which cannot be activated even if you have a valid serial number.
CS5 is due to be killed off by Adobe soon as well.
So even in the highly unlikely event yours is deactivated and comes with a legit serial number, you soon won't be able to activate it or use it anyway.
Better to invest in current supported versions of the Adobe apps.
Or check out the latest Photoshop Elements if you do not want a subscription product.
I totally agree with John. It would be wise to go with the online version.
In addition to what others have said, you need to transfer the photoshop cs5 license to you by the
seller and you filling out this form: