Vendor Tipping Etiquette

I am in the process of figuring out how much to tip our vendors to help manage our budget. I had my makeup trial done the day of my engagement pictures and it didn’t even occur to me to tip her for the “trial”. I will be using her for the wedding day for myself and my bridesmaids . I paid the entire amount for all of the services a week before my trial when I signed the contract. Which looking back was risky on my part, but she did a fantastic job. I just didn’t think to tip her for the trial and the wedding separately, I was intending to tip her 20% the total cost the day of the wedding. But now I just feel sick about it. I did tip my hairdresser for my hair trial for the engagement pictures, but I am going to be seeing a different stylist. So I am saying all of this to ask, how much and when do you tip your vendors?