one gun shop employee said they were generally a very unsafe gun and he wouldn't recommend shooting it.
You encountered a ignorant gun shop employee.
Both the 6.5 and 7.35 Carcano is safe to shoot, just follow common sense, make sure it has correct head space, barrel/bolt is reasonably good condition.
Surplus 6.5 ammo is generally very poor. The 7.35 is better if it has been stored properly.