While it always best to negotiate SLAs in a competitive environment, it's often possible to negotiate them mid-contract. Here's a good starting point for quality-of-service metrics:
1. Specific competency requirements. Could be language skills (Indian call center providers administer language fluency tests), or skills competency tests, with minimum requirements or tenure. Microsoft certifications are an excellent example.2. Customer satisfaction surveys. Make sure they are generally trending in the right direction
3. Employee retention/turnover objectives; at least for key personnel
4. SLAs for response time, first-call resolution percentage, etc
5. Escalation procedures, perhaps with second-tier responses going to your in-sourced personnel.
6. Reference checks. Prior to signing the agreement, rigorous reference checks with similar clients and due diligence (including 'secret' calls as a customer) should be conducted.