To make sure that the auditor is knowledgeable and delivers quality results, make sure to get acquainted with the company before agreeing to work with them. Do your own research, there are always reviews and client testimonials available for review.
Aside from that, check which projects the company audits most often, and what languages are the most requested. This may help you find not just the best auditor but the best one for your project. Make sure to review the existing audit reports, since they have to be thorough, easy to comprehend, and even appealing in terms of design.
DeFi Security Alliance offers the easiest way to navigate through many auditors on the market.