That's your choice of course as a big seller.
I've bought several boats, and numerous houses, and I've never put up the "recommended" earnest money
If a couple thousand isn't enough to convince you I'm a serious buyer, and hold the boat a few weeks while I inspect it, and raise the cash, you can wait for the next buyer.
On the big ticket items I've sold
I've never held a buyer hostage.
In several cases after verifying funds, I didn't even cash the check until the option period expired.
As a seller it's zero risk. Worst case, I slowly accumulate back up buyers while waiting for the first one to make up his mind.
There may be a legitimate business case for wanting a $15,000-$30,000 deposit, but I've never seen it in several big ticket sales on both sides of the transaction.
Depending on the State getting the deposit back can be a hassle.