Look, negotiate and if there is no 'give' in the price of the first flat, then drop out of the deal and buy the cheaper one.
Selling property is a business deal overlaid with emotion. If you buy the flat you have offered for and something else comes up and you do not make the change, you will never settle because the price you paid for the first flat will rankle and you will always be making invidious comparisons between the two flats.
Is there such a thing as delicious ready meals?