You may feel rude but at the end of the day it's your business. If they come back the second time you should give less information than you provided on their first visit, but tell them you can give them a more thorough explanation if they booked an appointment. Alternatively stop giving away free information. When someone calls/comes to see you with their problem, you can respond with

"That sounds like a very complicated situation. If you would like to book an appointment, we can discuss your current situation, and work out the best thing for you".

This way they know you are invested in their story and want to help, and you have offered your services, and you have not provided them with much information.

Giving away free information is one thing, but don't start filling out papers for people. You need to charge, or else you're just a charity.

You may feel rude but at the end of the day it's your business. If they come back the second time you should give less information than you provided on their first visit, but tell them you can give them a more thorough explanation if they booked an appointment. Alternatively stop giving away free information. When someone calls/comes to see you with their problem, you can respond with

"That sounds like a very complicated situation. If you would like to book an appointment, we can discuss your current situation, and work out the best thing for you".

This way they know you are invested in their story and want to help, and you have offered your services, and you have not provided them with much information.

Also, giving away free information is one thing, but don't start filling out papers for people. You need to charge, or else you're just a charity.