Answer
(Fatwa: 543/325/L=1434)
(1) You did not write the detail of online business. However, if the online business is done before taking it into possession i.e. after buying the goods it is sold before taking it into possession then it is not lawful to deal in this way. The holy Prophet Muhammad (صلى الله عليه وسلم) has forbidden selling an item before taking it into possession.
(2) For this, you should get a set of “Islam Aur Jadid Ma’ashi Masail” by Hadhrat Mufti Taqi Usmani Sahib. It is very good and consists of eight volumes. It deals with most of the old and new rulings regarding business.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband