Assuming you are registering with HMRC as an employer and operating PAYE the main pitfall is him or her not turning up when you need them
If you aren't doing that on the basis that this person is self employed your biggest pitfall is getting caught by HMRC and having to pay the deductions you should have made from pay and a possible fine.
I've taken the plunge and finally offered a casual contract to a former colleague who I've got back in touch with - not someone I am personally friendly with, but someone who I believe can do the job I want done, which is to work with me in the tea room during busy periods, and be able to cover for me on occasions so I'm not completely tied to it 6 days a week.
I've got access to HR support through Chamber of Commerce membership - and I'm confident that I can put all the paperwork side of things in place, but what else do I need to know? There will be no guaranteed hours - and the staff member is under no obligation to take hours I offer. Is there anyone who employs casual staff who can tell me what the pitfalls are?