The first and basic advice is: Do not buy the clarinet before you consult your teacher. You do not know which size, type and system of the clarinet (ordinary German or French Boehm) your teacher requires and how many keys the clarinet should have.Good and experienced clarinetists can not play a bad and defective clarinet, not to mention beginners.
When buying the clarinet it is good to stick to the saying: I am not rich enough to buy cheap things.A beginner should have a new and high quality instrument. It would make his job easier.
Sweating of fingers is a common occurrence when you perform. They slip off the keys. Therefore, manufacturers produce clarinets with nickel or silver plated mechanism. Silver plated, however, are more beautiful, and the fingers on them slip less.
If buying a used instrument, also consult the teacher. Such an instrument could have worn wood and worn mechanism. It can produce bad tunes and be cracked, etc..
Taken from my book