In my limited experience piston slap is not a common complaint with these engines although that dos not rule it out. On the other hand, my Subaru Forester has slapped away alarmingly when cold for the past 230,000 miles, so John's suggestion to drive it may be a good one.
Valve train noise will often go away when warm also, so make sure you positively rule out that possibility.
Also, again in my limited experience, piston slap is usually caused by a fault in the piston. If it is, it's not that hard to replace one and new pistons are probably available, depending on size, although you might have to buy a set. If compression, oil consumption, oil leakage and oil pressure are acceptable, I might consider that option.
Tom