Why not? If you want the thing they have, keep calling.
Only if they're not in the business of offering customer service for a really expensive purchase. I'd find it kind of offputting (in many ways, not just impoliteness) if someone I wanted to throw £10k's at couldn't even find the time to call me back.
Fair but just because the purchase price is high, doesn’t mean they’ve got a customer service department. They’re probably just a few people in what is ultimately a pretty niche industry. The person answering the phones is almost certainly someone also doing the work etc.
Only if they're not in the business of offering customer service for a really expensive purchase. I'd find it kind of offputting (in many ways, not just impoliteness) if someone I wanted to throw £10k's at couldn't even find the time to call me back.