All toning is real. Your question really should be, is it natural or artificial? Apparently, PCGS thinks it's natural or it wouldn't be in one of their slabs.
I don't follow Kennedy half dollars, so I can't help you on value. It's a nice coin if you like toning.
There are a couple pricey varieties of the 64-D, so you may want to check that. Otherwise, $250 seems pretty steep to me. The toning is descent looking and I think natural.
There are a couple sold listings of the same grade coin for $40-$50 on ebay, and a lot under a $100. So you'd be paying quite the premium for the toning. (but I'm no expert on how much toning can increase the value of a coin)
PCGS has them at $150 on their price list, but they go much cheaper than that usually. Add in the toning and $125-150 would be about it for me.
Perhaps I've misunderstood, and at least I hope I did, but are you saying that you think it okay to crack out the coin and then try to return if YOU decide the toning is "fake"?