It's possible that there's still some old finish, but maple can be a difficult wood to stain, leaving you with a lot of splotches.
Rub surface with rag dampened with paint thinner - this will highlight any areas with finish still on them.
There are a number of ways to prevent splotches depending on your finishing schedule and/or desired look. The most common technique, is to seal the surface usually with a diluted shellac solution. You can then either directly apply color/finish causing it to sit on top of the sealer, or lightly sand the surface then apply color/finish. If you sand the surface, you'll remove the shellac from the higher density wood fiber areas (knots, for example), while leaving the shellac in the less dense areas. This causes color/finish to sit on the less dense, sealed areas, while being slightly absorbed by the more dense areas. Since the more dense areas don't really absorb that much color/finish, you end up with an even color coat. You can test this on the inside of a drawer to see if you get the results you want.
Another, somewhat easier method is to use a gel stain. Apply, remove excess, and after 15 minutes or so determine if this is a look you like. If too dark, wipe surface with rag dipped in appropriate solvent (water for water base stain, paint thinner for oil base stain). If too light let dry and apply another, lighter coat of the same (or different shade) color.
Bob "Boardman" Borders