A very good question, and not one for which there is an easy answer.
A few thoughts, but by no means a complete answer.
First of all, would you let your family fly with the person. But as you say, it's not that easy.
Are their landings perfect? If not, can they spot the errors, and do they learn from their mistakes and improve?
Do they know what their limits are? Do they honestly believe they can fly to the south of France after a 6-month layoff? Or are they planning on sticking in the circuit or the local area until they're a little more current? If they are planning on a more difficult trip, are they aware of the issue, and asking you for a checkout which is tailored to that trip, or do they expect you to sign them off to go to the south of France after one circuit?
At the end of the day, it comes down to judgement, and it takes experience to build up judgement. But remember that this individual has, at some point, passed a test and proven that they are competent to fly. If they are clearly not competent then this must be pointed out to them, but in my experience so far it is only a very small minority who are not competent after a short checkout if the break has only been relatively brief.
FFF
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