What should I think about durability or maintenance of a decent (Yamaha/Kawai/Roland) digital piano or hybrid piano? Does hybrid/digital seem to differ in reliability? (Or do brands?....)
How should I weigh buying a new-ish model used (against buying unused), as it might have a history and lack the 10 or 5 or ? years' warranty? (Or are the warranties not limited to first purchaser? Do the warranties even seem to be useful?)
What might I anticipate of lifespan needing to do for repairs or maintenance or for keeping a good environment for a digital?
Digital pianos are quite like cars: they depreciate horribly, are produced via automated processes, and are now much more reliable than they were 20-30 years ago. I would anticipate at least a 10-15 year life span, with perishable part replacement costing you around £200 per decade (anecdotal).
My goal in both cars and digital pianos is to buy a fairly new unit (<3 years old if possible, certainly under 5 years old). One can inquire about whether it's been gigged with, what sort of home it's lived in (is the house a smokers property?), you can ask if they've ever had it fixed (always good to see if someone's honest, and reassuring if they are).
Nothing is better than a substantial test of a used instrument: make sure everything works, make sure the action is consistent across the 88 notes, know what functions to test in advance etc.
Bear in mind: often, if something is going to go wrong, it's likely to happen when the instrument is first used i.e., something escaped the attention of Quality Control, or, something damaged the instrument in transit. Therefore, if there is a good reason for someone selling an instrument, it's young etc., and it survives a full lengthy targeted test, then you've probably got a good deal.
On the other hand, it it looks in poor condition, has an uneven action, has issues with the damper, with the dynamic consistency etc., then you probably want to avoid.
I think if people felt confident that they would get a straight deal used, most people without a great disposable income would prefer used, as one doesn't lose anywhere near as much money on depreciation buying used.
An MP7 and now the MP7SE cost around £1300-1400 new.
I brought my MP7 (1 year old) for £750. I sold it for £700, 2 years later.
I brought my MP7SE (1 1/2 year old but hardly used) for £850.
One's losing £500 in the first year of ownership and taking the risk on the new instrument arriving broken.
I want to be cautious too though: I'm forming a relationship with the seller in advance by asking pertinent questions and getting to know a bit about them. I get a vibe for the seller and if it's a good one, I do my instrument research and ask to test with view to buying! I know what I'm doing in advance of testing an instrument. I'm not taking the wrong kind of chances/risks. Also, I'm aware I could lose out. When I test an instrument, even if I think it's going well, I go back to my list of things to test and make sure I get it all done.