When to book survey?

[Junioh]

We've just constructed a chain, and keen to get a survey done. However our buyers haven't booked one yet and I'm worried about paying out for ours if they then pull out after.

What do people normally do?

We waited until we had our mortgage offer in place, just in case any issues there.

I had my survey done before my buyers because if it turned out to be awful I could pull out of the sale. It's tricky balancing everything though.