Milo...This has been much-discussed here in the forum for years. You should already know it's a no-go. There may be a few tiptop providers who are reliable and will come through, but, wait, even a few of those have no-showed, too, after receiving a deposit!!
I can understand frustrated providers trying the deposit remedy after six client cancellations in a row, but it's part of the business and savvy clients should resist advance deposits