Extinguisher servicing contracts — what to look for?

For firms that outsource extinguisher servicing: what has made the difference between a good contract and a painful one? BAFE SP101 accreditation is the baseline, but beyond that: - Fixed-price or per-unit pricing - Inclusion of refill or replace in the contract - Reporting quality (digital logbooks vs paper) - Same-day response SLAs Who do you use? Happy to share recommendations.