It's always hard to tell about heads looking at pictures.... You need to see them personally and have a flashlight and magnifying glass to be able to look for gap damage and pitting and to be able to judge the amount of wear the heads have seen.
The only accurate way to tell the remaining head life is to send the headstack off to John French or Sprague Magnetics and have them do the necessary measurements with their specialized equipment.
From the pictures through, I'd say these have seen a good deal of use, but seem OK.... There is a wear pattern but it's hard to see if there's a flat area or if the wear pattern is more rounded. Rounded is good - better tape-to-head contact in the head-gap area..
I have 2 Studer A-810's here in my shop at the moment - 1 is in good shape the other is junk.... bad eproms, noisy supply motor and so on... the bad a one a client bought off of eBay (good condition said the seller!) the other my client went to look at personally and recorded tones and ran the machine for a few minutes.
So... if you cannot personally see and use the machine before you buy it you need a good written statement you can return the machine if you find it isn't what you want and get a refund. If the machine is local to you, record tones and make sure they play back fine and are stable.
Take a look at my web site - Analog Rules!!! Pro-Audio Parts and Service
. There's a link to a page on the site showing pics of 'bad heads' and though the examples are 2 inch heads for the most part, the same thing applys for 1/4 inch heads.
A really worn head will cost you hundreds of dollars to replace.... BUT the odds are you won't be using the tape recorder every day for hours and hours, so even a worn head might last you a few years.
The Studer A-810 is a fine machine.
Don't worry about the Center-Track time code...