We just got an offer accepted for a property. The vendor requires us to book a mortgage survey within the next few days, otherwise they'll show the property to other people. They argue this is to show that we're committed to buying. The thing is they have not found their next home and they literally just started looking. We'll have to pay for the survey without knowing what's gonna happen. We're also worried that if we pay things upfront, the vendor will have guarantee that we will not walk away and they'll slow down their home-hunting process.
Is the vendor's requirement normal? What should we do?