If I was the owner, I would have returned it. I hate to keep other people's money, even for a second.
And if I was the OP, I wouldn't expect to get it back.
Always be nicer but keep low expectations of others. You will be more content this way.
Right on! In fact, as a seller I would say:
'Keep your deposit, I'll give you the first bite of the apple.. if a higher offer comes along I'll call you and either you'll buy it or I'll sell to the other guy.. but I'll take your lower offer first. Sound reasonable?'
This approach will create urgency and cause the sale to happen faster. Arbitrary 'holds' for time periods only server to freeze the process which can cool off both buyers in the end.