Sometimes owners won’t provide much information about their tenants, etc. until they know you are serious about the building. Or, they might want you to sign a confidentiality agreement in which you agree not to share any information you learn about the building. This might require you to put out a binding letter of intent to the seller with a number of contingencies.   If the building you want to buy has many tenants you will also need to estopple letters from each tenant. This letter allows you to review what the tenants believes the terms of their lease is verses what the lease states. It is important to match up these documents to make sure there are no surprises after the closing.