Boutique M&A Interview

It's going to vary a lot from firm to firm, but based off of my experience interviewing (various southeast regional firms) see below:

• Have a good why - Fit is going to be key here especially at a smaller firm where a good and / or bad apple will have a larger noticeable effect. My story usually reflected my ties to the. Southeast as well as something specific about the bank I'd be interviewing at (e.g., industry, focus, etc.).
• Still practice your technicals - You still need to know your technicals at a basic level. You probably won't get anything too hard, but you could still get a good amount of questions (e.g., how the three statements flow together, valuation methods, walk me through a DCF, etc.). 
• Misc. - I've been asked brain teasers (e.g., how many phone booths are in NY) and economic thoughts (e.g., what's your take on what's going on in the economy), so I'd still cover your bases there as well.

Overall, I think you should be fine. I'd focus more on the fit / qualitative questions rather than technical questions though.