Look at the roof-covering materials on neighboring homes. If they’re mostly tile, your’s is proabably OK. Disclaim responsibility for confirmation of the ability of the framing to carry tile. You have no way of knowing.
Older tile will sometimes show efflorescence. High quality clay tile is almost like glass… extremely vitrified, and will not absorb moisture. Lower quality will absorb moisture, delaminate or flake, and exhibit microbial growth over the years, especially in freeze-prone climates. Some discoloration that you’d swear is mold is not (take my upcoming roofing video courses)
Concrete tile lasts pretty well. As Gerry mentioned, flashing, fasteners and improper installation are what to look out for.
Yep… look for bad flashing. Sidewalls should have continuous pan flashing with a raised edge to form a water channel.
… and good inderlayment. Tile usually has 30 lb underlayment or better specified by the manufacturer and code, but not always. If you see 15lb. recommend a specialist inspection.
Look for (and call out) exposed underlayment
Cracked, broken or missing tiles… call 'em out. The older the roof is, the more fragile. You don’t have to walk tile roofs.