BUYING A PIANOLA

Pianola's (Player Piano's) generally were made from about 1905 until 1935. Most were made between 1917 and 1929. Anything before about 1910 is likely to not take the standard 88 note roll. Patent dates stamped into parts are not an indication of when it was made. A few Pianola's were made in the 60's until present - these are smaller with many plastic parts.  Pianola's are dated by their serial numbers many of which are available online.
Most Pianola's come from America, while most made here use American player actions inside. Large stores often rebadged Pianolas to their own name - e.g. Paling's rebadged Laffargue's from the U.S. as 'Victor' (Amphion action).
There are only about 60 pianola mechanism manufacturers which are found in many hundreds of piano makes. Some piano companies made their own pianola mechanisms while most bought from larger manufacturers. For example most Beale's use Amphion actions from the US (earlier had Otto Higel), Gulbransens made their own pianos and their own pianola actions.
 The Pianola mechanism maker (not the piano brand) can be found either on a plate in the spoolbox, on the stack or pedal mats. Some do not say.  Photos of the inside can help identify makers.
The Pianola mechanism is quite separate from the piano mechanism and may not be functional even if the piano plays well by hand. It consists of hundreds of small moving parts, many of which are leather, rubber cloth, zinc/lead  metal and rubber tubing which are perishable with age.
Buying Restored or Working:
A restored pianola should pedal through a roll easily, not be a workout for legs. The roll should move smoothly and not speed up or slow down when pedal pressure changes. All notes should play evenly for a given pedal pressure and correctly repeat trills in the roll.
Tracker systems keep the roll in line with the tracker bar holes and should work automatically and correctly otherwise the rolls will wander and wrong notes will play.
Unrestored or not working:
Be aware that the cost of repairing a Pianola mechanism to proper working order is at least A$2500. Unfortunately this can outweigh the value of the instrument particularly if the piano itself or the case needs work too.
Some makes of Pianola are easy to restore and others are very difficult with most restorers refusing to do them.
Easy Pianola actions to restore include Amphion, Aeolian, Standard, Strauch, Autopiano, Otto Higel later unit valve Gulbransens.  Difficult one include Hupfeld, Earlier Gulbransens, Schulz, Simplex.
Beware of pianola's which have parts missing - many had the pianola action removed and thrown away.
Also its extremely rare to find an 'easy fix', eg the "tube has fallen off" or "just needs a few tubes replaced".
Rubber cloth and tubing generally have a useable life of 20-30 years. Also many metal parts including lead tubing deteriorate with age and fall apart.
Reproducing / Electric pianola's:
These are a special type of Pianola which plays the expression automatically by specific rolls with coding on the edges, usually driven by an electric pump.
They are rarer and more valuable than normal pedal models and while they need their own special rolls for automatic expression  they can still play 88 note rolls. Common types are the Duo-Art,Ampico & Welte. Beware of pedal only models of Duo-Art and Ampico as they have a much simplified system installed and, although they can play the expression rolls nicely, they do not have the same value as an electric model(and often the expression system has been removed). Restoration of an electric Reproducing Pianola is normally twice the cost of an 88 note pedal player.
A 88 note Pianola with a modern electric vacuum pump installed is not a Reproducing Pianola and usually the pump is there because the mechanism is so leaky it cannot be pedalled.  
An excellent book on the subject is Player Piano - Servicing and Rebuilding by Arthur Reblitz.