"Best time to buy" varies greatly depending on one's goals.
Frequent pre-closure situations are listed properties with a Realtor, as the homeowners may attempt to sell before reaching foreclosure and/or work a Short Sale situation out with their lender. Buying then may be a great situation if the property in question meets all your Wants and Needs.
Once in REO, the lender doesn't want to keep the property, of course, so making offers then can work to the ultimate financial advantage. But waiting until then risks losing the property to another buyer, so if it is 'the ideal new home" for you, you may not want to wait until the 11th hour and risk not winning your offer.
Auction down payment percentages are usually pre-set and in the notice of auction. The value set is usually 10% of what the market value is deemed to be.
Down payments offered in pre-foreclosure or for an REO property listed in the MLS are negotiable items and your Realtor representing you can counsel you on that we you contemplate composing an offer. If your down-payment question was related to down payment minumums to be eligible for mortgage financing programs, then that can easily be determined in conversation with a mortgage consultant based on your individual financial situation.
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