I would suggest establishing a personal policy of accepting only one romantic proposition per person-you-are-not-already-dating per week, or something along those lines. That way, if someone offers to change immediately, you can simply explain that you will not consider any such offers from them until the given time period has elapsed.

If they are bullshitting (as seems likely) and have little or no intention/ability to maintain such a change, the delay is enough that they will look elsewhere for short-term satisfaction; if their interest is genuine, persistent, specific to you, and the problems are as superficial and trivially resolved as they claim, 168 hours should be more than long enough to implement such a solution and clear your short-term memory for a new 'first impression.'