G.R. No. 195166 - Spouses Abella vs. Spouses Abella

Petitioners Spouses Salvador and Alma Abella extended P500,000.00 to respondents Spouses Romeo and Annie Abella on March 22, 1999 by way of an acknowledgment receipt stating the sum was “payable within one (1) year from date hereof with interest.”
Respondents acknowledged receipt, admitted two payments of P100,000.00 each (June 30, 2001 and December 30, 2001), and claimed to have paid monthly “interest” at 2.5%.

Respondents asserted the P500,000.00 was capital for a joint venture: petitioners would receive 2.5% per month, respondents a 2.5% service fee, and the one-year term was merely an exit period if unprofitable.
They alleged the joint venture yielded only P200,000.00 in collections, leaving P300,000.00 unpaid.

On July 31, 2002, petitioners filed Civil Case No. 6627 for sum of money and damages; respondents answered with counterclaim and motion to dismiss.
The Regional Trial Court (Dec. 28, 2005) ruled in favor of petitioners: P300,000.00 principal plus 30% per annum interest from July 31, 2002, litigation expenses, and attorney’s fees. Motion for reconsideration denied (Mar. 13, 2006).
On appeal, the Court of Appeals (Sept. 30, 2010) reversed: held no valid interest rate was stipulated, treated all payments as principal, found overpayment of P148,500.00, and ordered petitioners to refund that amount with 6% interest from decision and 12% upon finality. Motion for reconsideration denied (Jan. 4, 2011).
Petitioners filed a Rule 45 petition before the Supreme Court seeking reversal of the Court of Appeals decision and enforcement of 2.5% monthly interest plus remaining balance.

Whether interest accrued on respondents’ loan from petitioners; if so, at what rate?
Whether petitioners are liable to reimburse respondents for alleged excess payments and to pay interest thereon.