Here is how I would do it:
- Ask him about his/her previous experience, how many plugins has he/she developed?
- Ask them what framework or format they follow.
- How much do they know about best practices for plugin development
- If you are starting from scratch, ask them how they would go about it and get a proposal (there is a structure they should follow)
- If you already have a plugin, have them take a look at it and get a list of suggestions for improvements.
- Generally, it is better to pay more for an experienced developer. It will save you a ton of money even though the hourly rate may be more expensive. The cheap inexperienced ones will cost you 10 times more because of lack of experience.
If they hesitate or don’t like any of the suggestions above or are not willing/able to provide it, move on. There are a ton of good ones out there.
Spending a little more time in finding the right developer, will save you headaches, time and money down the road.
Hope this helps
Founder at WordPress Spell check