What makes a multiple 'reliable' — which quality criteria do you check?

Quality-of-multiple checks:

• Dispersion in the comp set: if the median is 9x and the range is 5x−18x − the comp set is heterogeneous and the multiple is unreliable. A range of 8x−11x − more robust.
• Consensus coverage: the multiple rests on consensus EBITDA — with <5 analysts covering, consensus is thin and possibly stale.
• Recent earnings volatility: if the comps regularly miss earnings, the forward multiple is unreliable.
• Historical multiple stability: if the sector multiple has risen from 6x to 12x over the last 3 years, the 'current' multiple may be in hype mode.
• M&A context: at what multiples have recent sector deals closed (cross-check)?