Most, but not all genuine figures are hollow-cast lead.  There are some genuine solid lead figures as well; although they were not made by Britains.  Not all cubs have a base but those that do have all or some of the words; "Copyright Cadbury Britain's Proprietors" (abbreviated) stamped on the base.  As well as forged figures some models can be either re-painted entirely or just touched up.  The vast majority of collectors do not buy these and as they do not command a price premium they can be picked up very cheaply; unfortunately the majority of sellers do not advertise the fact that the figures have been over-painted and only your personal experience as a collector will enable you to develop a nose for what is right.  In life if something is too good to be true then it probably is!  Some cubs are now over 70 years of age; as toys for children they will show signs of having been loved but some figures have survived in sewing boxes etc and can be in excellent condition. 

Generally speaking figures were dipped into a paint colour that suited that of the figure and thus made it easier to finish off by hand.  e.g  Dumpty Doo Ducks were dipped in yellow paint whilst Freddy Frogs were dipped into green paint.  The other colours were then over-painted. If the models have a chip in the paint then the base colour can be seen.  This information can be a useful way to identify a re-painted figure; also look out for out of place contour lines in the paint or blotches in the paint, which will identify over-painted chips.  It becomes all the more confusing when one learns that at Christmas Britain's employees were allowed to take home figures that had been rejected by quality control and so some figures that appear unusual are in fact quite genuine.

Be aware of figures which have a match-stick join.  This is a ruse known to all school boys who fixed their toy soldiers by inserting a match-stick into the broken hollow legs to create a quite seamless repair.