The risks of hiring someone who is overqualified are well-known. They’ll quickly be bored and leave. They will probably hit you up for a raise sooner than expected.
These are possibilities, but what about the upsides? This article points out some potential benefits.
They may catch on quicker than others. They might do the job faster than coworkers and then use the extra time to contribute in even more valuable ways.
If they are applying for your job, and say they want to do the work, you may want to take them at their word.