Prop strike effect on resale value?

As others have stated, you need to follow the engine manufacturer's
instructions following a prop strike or "sudden engine stoppage".
Usually this calls for inspection of the crank runout at a minimum. Some
call for engine teardown and magnafluxing parts. Still other engines
require replacement of certain parts like counterweights, camshaft
gears/bolts and other timing gears. I believe it depends on the make and
model of the engine, although others more familiar with this can chime in.

As the fleet ages, trainers especially can be expected to have SOME
damage SOMEWHERE in their history. Proper repairs (as evidenced through
documentation and inspection) and time appear to mitigate any devaluation.

My '74 Cherokee 140 did a ground loop in 1975 at 398 hours since new.
Tore down engine, inspected/replaced all the necessary stuff, replaced
the flaps, stabilitor, and an outer wing skin. Spars checked O.K. All
replacements and skin work flawless (as inspected by several wrenches
over the years). I now have 2600 hours on it.

Will I take one penny off for a 30 year old repair that is invisible,
one whole engine ago, and has withstood the test of time. Nope. And I
will have PLENTY of other buyers who will snap it up if someone insists
on a lower price for the damage history.

Now, a recent prop strike, that is another matter. The opportunity for
hidden or latent damage is quite a bit greater. Eliminate the engine
(via overhaul or replacement), overhaul/inspect the prop, and inspect
the rest of the bird and you probably won't care as much. Don't do those
things and I would personally consider the engine and prop as trash. I
would still insist on a careful inspection of the rest of the bird.

Others may disagree, but it is your money and risk.

Good Luck,
Mike