Is it permitted to shave before Shabbat during the three weeks? Does the Halacha become more stringent during the nine days?

The Ashkenazi custom is not to have hair cuts or shave from the seventeenth of Tamuz until after Tisha Bav, including Fridays. (Kitzur Shulchan Aruch 122, 2) The Sephardi custom is not to have hair cuts or shave from the Sunday of the week of Tisha Bav. (Shulchan Aruch 551, 3) From Rosh Chodesh Av things do become stricter (for all details see Shulchan Aruch 551)