What form is used by a seller who wants to utilize an existing survey while ensuring the boundaries have not changed?

The correct answer is the T-47 Residential Real Property Affidavit. This form is specifically designed for situations where a seller can verify the property's boundaries and affirm that there have been no changes since the date of the last survey. The T-47 affidavit serves as a legal declaration that the seller is affirming the accuracy of the existing survey, which can simplify the transaction process by eliminating the need for a new survey if the boundaries remain unchanged.

The T-47 helps to provide assurance to the buyer and any lenders involved that the property lines, as defined in the original survey, are still valid. It acts as a protective measure against disputes that could arise over property boundaries during or after the sale.

In contrast, the other options such as the T-123 Survey Certification, Acknowledgment of Boundary Lines, and Boundary Assurance Document either do not specifically cater to the context of an existing survey being utilized in the same manner or may involve additional complexities and requirements that are not necessary when simply relying on an existing and unaltered survey. Thus, using the T-47 is the most appropriate and effective choice in this situation.