Whose painting is it? Who saw it and booked it first or who paid for it first?

You  wanted to buy a painting and were told it was ‘under consideration’ by someone else, but that person had not made a deposit, so you could buy it.

You  wanted to buy a painting and were told it was ‘under consideration’ by someone else, but that person had not made a deposit, so you could buy it. You  paid and planned to pick it up at the end of the exhibition. Days later, the gallery said it was returning your money because the other prospect had purchased the work. You later learnt this buyer wrote a positive review of the exhibition. Did the gallery act ethically?