It often goes something like this...

"That house was listed for a sale a few days ago for $435K and I could probably only afford to pay $425K.  I'm sure the seller would not accept my $425K offer, so I just won't make the offer."

"I know that house has been on the market for two months priced at $650K without a price adjustment, but I'm sure the seller would not be willing to sell for $625K, so I won't even make the offer."

"Even though that house has been on the market for a few months, they probably still wouldn't accept a full price offer because I would need to include a home sale contingency, so I probably shouldn't make an offer."

In almost all cases, I recommend that all three of the fictional buyers above go ahead and make the offers that they chose not to make because they assumed a seller would say no to their offer.

Certainly, a seller might really say no to your offer, but that's OK.  If you never actually make the offer, you'll never have a chance to find out if the seller will say "no" -- or whether they would say "yes" or "no, but how about..."