I would start by asking them about their friends. What are their friends like? Who do they hang with. What have their friends suggested and have they taken that to heart. You might get an opening there.
If that doesn’t work, try asking them what are they looking for in a girl. If they talk about looks in a girl, then you have an opening there as well. Because you can ask, what does that mean? What does pretty mean to you? What does a good dresser mean to you? What does a nice smile mean to you, what does appearance mean to you and so on?
Then you compliment them on their honesty and the things you can compliment them on and gently move on to the things you can help them with. Would you be open to a new look? Girls put a lot of effort into looking good for their dates and most young men show their appreciation by doing the same. Your look is quite unique but a little too unique for most girls, do you think we can tone it down a bit? And for the other guy, “You know you really have a winning smile, but a trip to the dentist can make it even better. It could use a little whitening and brightening and then no one will be able to resist you.