Pretty simple - if these people are friends, then discount them whatever you feel comfortable off your normal markup. If they are just random people, discount less. You need to weigh the cost vs. benefits of any transaction you are discounting. Is there a potential for additional full price transactions or possibly referral business with this request? If so, I have found that keeping your options open and being flexible with your pricing structure allows you to explore potential avenues that might otherwise never be opened.