I am single and claim 4 on my W4. I recently had a commission due in the amount of$2671.00. Almost $1000.00 were taken out, is this correct?

Irrespective of what you have put on W4, bonuses and other supplimentary payments are subject to statutory withholding (i.e. by law) at 25% for Federal Income Tax. SS and Med are also withheld. Many states also have statutory withholding on bonuses.