Give the developer a simple task that is work relevant and 24h. If the person does it in 5m using some fancy trick, then you know they're a problem solver of h

Give the developer a simple task that is work relevant and 24h. If the person does it in 5m using some fancy trick, then you know they're a problem solver of high calibre. 1h-5h: They are probably adequate. 24h: junior or bad. Ask them about the trad offs they made. The 24h guy may not have made any, and may be the perfect maintainer. The 5m guy must have made some. Ask for their reasoning. It may be the reason to hire them. It may be the reason not to. Feel free to pay people for being tested.