How can I politely turn down a potential client?

I recently met with a bride and groom about photographing their wedding day. As the conversation went deeper I got the feeling that we just weren’t going to mesh well with each other.

I keep my prices low because I’m just starting to dive into the wedding business. This couple wanted an even lower price then my lowest available but at the same time they want million dollar quality.

By the end of the meeting they said they would contact me within the week (the amount of time I hold a date for clients without a deposit) and let me know their decision. Honestly, I just don’t feel like it’s a good fit. The personalities don’t match up, the expectations are very high and I worry that no matter how great of quality photos I provide to them, they’re impossible to please.

Assuming they want to book me (and they did hint several times that they want to) how should I go about telling them I don’t want to do their wedding? As much as I hate turning any business away, I don’t want to set myself up for failure this early on.