If you do not plan on charging for the service or are not planning on making money off potential pricing differences (arbitrage) I would think that there are no problems buying from the exchange and having friends or family pay you back. Even if family gave you a little incentive for your help, that shouldn't be a problem. Notice how I never say you should offer them a service, if you are doing it this way it has to be (1) for free (2) for family and close friends and (3) as a helping hand NOT a service.
If you do plan to be a broker of sorts and facilitate exchanges for a fee or percentage, you should create a business, with all the paper work that goes along with that. It is not difficult, and if you're only doing a little bit of brokering, you'll not pay much in taxes and certain costs (such as computers used) could be written off for tax purposes.
You should have no issues if you follow these guidelines:
- buying for family and close friends
- no fees or charge
- offer help not service
If you want to make money doing this, you should:
- incorporate a small business
- come up with a defined fee structure
- keep detailed records of all services and fees charged
- file taxes for the small business
Hope this helps!