Where is this condo located? It is going to be very expensive to heat with electric radiant heat.

Not to mention heat rises... better to have it on the floor if you have it at all. A heated ceiling would be counter productive.

If interested in the house it needs an entire new system. And a markdown for such. Radiant heat in the ceiling is pointless. You and everyone else knows heat rises, apparently the few dinks back in the day that got away with installing these like that didnt know. Imagine how much energy has been wasted... the shame.

Has a ceiling with radiant heat installed in the 60's and 70's ever "collapsed" due to the heat expanding and contracting the sheet rock and causing the fasteners to fail?

Where is this condo located? There was a system of electric radiant ceiling heating sold in the province of Quebec, Canada in the 80's (i don't know if it was sold as early as the 70's though) that is no longer sold and has been banned because it started numerous fires due to its bad conception. It was a sheet similar to modern radiant floor mats that you would staple to the joists before hanging drywall. I would have the ceilings looked at by an electrician before buying this condo.