Originally posted by TangoMike I hope I'm not being a pest, but I really appreciate the opportunity to learn from the varying perspectives of experts.
You're not being a pest at all... Experts we may not be, but there's good experience within these forums, and it's worth researching a purchase like this properly
There is always
some risk in buying a used camera without a warranty - no doubt about it. But, consider the following:
(1) The K-5, K-5II, K-5IIs, K-3, current K-3II and K-1 are all "flagship" models - they were / are top-of-the-range cameras designed with heavy use in mind, and high shutter life stated in the specifications.
(2) Models such as the K-30, K-50, K-S1, K-S2 and current K-70 have no published estimated shutter life data. You can argue that these entry-to-mid-level models are less-well-suited for long-term heavy use (although all are excellent cameras).
(3) As has already been mentioned, the K-30 and K-50 are known for potential aperture mechanism failure. The majority of users remain unaffected, but too many have had the problem to ignore the possibility, and reports suggest that it can be age-related rather than being due to heavy use, with some bodies failing after only 1,000-2,000 photos in extreme cases. It's possible that some K-S2 bodies may have been affected too, or may be affected in future. We don't know if the problem has been resolved with the K-70, but it comes from the same lineage. If I was buying a new K-70, I would want the longest extended warranty available, just in case.
(4) Whilst few, if any, cameras (from any manufacturer) are entirely immune to the odd problem or two, the flagship Pentax models (with the exception of the K-1, released just this year) are all long-established and fully proven - there are very few known problems. It's a reasonable assumption that a used-but-not-abused copy has already displayed any design or manufacturing-related problems it may have and has been fixed, so it should continue to operate well for some considerable time. In this way, a slightly-used camera can be really good option, as it's a known quantity. So long as you ask the seller to disclose any current or previous issues, frequent or intermittent, I'd suggest the risk of the camera failing is pretty low.
(3) A used K-5 might set you back around $350 (for just the body - no optional accessories such as battery grip, lenses etc.). That's just over half the current cost of a new K-70. If the camera were to develop a significant problem, I'd guess you could sell it - with full disclosure to the buyer - for $150, leaving you $200 out of pocket. Even if you paid out another $350 for a replacement K-5, your total investment would be $550... still considerably less than a new K-70.
I'm not saying you shouldn't buy new, and I have no doubt you would be delighted with a K-70 - by all accounts, it's an incredible camera, and for peace of mind during the warranty period, you can't beat that option. But if you do your homework on the seller and the camera, a sensibly-priced used K-5 can be an excellent value, limited-risk proposition.