回複：請問私底下幫人做點事收了1000刀的私人支票要報稅嗎？對方隻

Ask the person who gave you the check if he/she reported this to IRS(he/she may report this so he/she can get credit to deduct his/her tax). If not, I guess it's up to you. Otherwise, you have to report it in case of IRS audit. Good luck!