There _ we got that out of the way! OK. Now let's look at when to use a Letter of Intent vs. a Purchase Offer. I am specifically going to address this when looking at buying an apartment building or commercial real estate. The standard contract used when purchasing real estate is called a Purchase Offer, or a Purchase and Sale Agreement. You probably used this to buy your own house or condo.
Buyer accepts offer and signs it, where offer acceptance is binding depends of the legal jurisdiction. For example English and common law differs slightly from American uniform commercial law on matters of offer acceptance and when performance becomes binding on an offer.