Any digital piano buyer's guide might offer some pointers on distributors and models, but few beginners can actually comprehend their subtle differences. Firstly, the best known piano-resembling instruments are: digital pianos, MIDI controllers and arranger keyboards. The main difference between the these instruments is their final goal: digital pianos are ideal for people who want the complete experience of an acoustic piano; MIDI controllers are normally used in studio recordings while arranger keyboards are the best alternative when it comes to live performance. Most models nowadays have some specifications from all of the three 'core' instruments, but it is ideal to know how and where you want to use it.
One more element that is not very well known is in regard with amplification. You ought to always take a lot of time to be perfectly up to date with the input-output specifications of your digital piano, or you will probably encounter a lot of obstacles when playing on stage. From RCA, MIDI, large jack or XLR, your output influences the type of cable you need and the kind of amplifier. In extreme cases you may also use adapters, but generally this not advised due to the fact that you will lose some of your signal.
To conclude, maybe the most important tip when buying a piano is to test the model you think of purchasing, experiment with it. Do not trust the opinions of others who state that a certain instrument is the best digital piano, for it most likely will not be suitable for you. If there is any universal tip regarding digital pianos, it is that all quality products have an 88-note weighted keyboard and can render a impressive range of effects and other expended functions.
You should also be sure to purchase quality products from well established distributors and always recognize cheap replicas.