Alternative experience might simply suggest that the pawls were stuck and needed freeing up. Experience also suggests that the only way to be certain is to open it up and confirm it one way or the other...
Not all freehubs are serviceable. I had an old Shimano Deore which occasionally used to freewheel thanks to sticky pawls. You couldn't remove it from the hub body. I junked it in the end, there's only so many times you can squirt GT85 into it before it gives up altogether.
LBS is a business, not a community service.
£50 for an entire wheel is pretty cheap.
If the freehub was knackered, and not repairable, the cost of buying a replacement hub then building it into the old rim with new spokes would be more than that. Shimano Deore hub c£25, 36 cheap spokes and nipples, c £20, labour £20 to £30.