“Let me check and get back to you” buys you the space to actually choose.

The phrase buys the one thing a quick answer denies you, which is a gap between the question and your mouth. Most bad yeses happen within about four seconds, under a hopeful face, before you have thought about Saturday at all. A delay is not evasion. It is the minimum room required to choose something rather than react to it.

Use it this week on the next thing you are unsure about, even something small. Then actually come back, which is what keeps the line usable. Over time people learn your answers mean something, because they were decided instead of extracted.