My previous comment is simply my view, as far as being put into practice and being able to ask 'five times' that's only reached negotiating stage so far and probably why it's stalled/ended.
For example, I have a domain which should/is currently giving me £120 a year in Parking revenue, even at five years that's only £600 when in reality I probably won't accept less than £3000 based on the name as well - depending on what mood I'm in and of course the financial situation.
I'll have to test selling items on the domain and see what that could bring in, because again that could increase the value to me.
I think it probably comes down to who you're marketing to. If you're just marketing on the basis of losses and quick turn around, then you're going to flip around the £100 mark. If it's to another Parker then you may sell for 2 years so as to reinvest whilst giving the buyer a noticeable 'recoup' period. But remember, CPC is set by outside forces, it shouldn't denote the value of a domain.
End users, well you can push the boundaries that little bit further simply based on the fact they're developing, running a business/service and will profit greatly. How you figure out an end user will come with practice I suppose, but I treat everyone as an end user as that's who I aim to market to.
Two years, three years or five years, it's personal choice. If you're losing money by selling for two years when you plan on keeping the domain for another ten, what's it worth to you and what's it worth to the buyer? but if you don't want the domain, don't have any plans for it and won't miss it after banking the sale, then two years would probably be acceptable.