"capital" used as in "preserve your capital of health". Used much more in French than in English, come to think of it.

Alternatives could involve notions of endowment, heritage or legacy, or store, storehouse, foundations, etc.

Basically, certification is in itself a durable asset - but its enduring worth is dependent on good customer feedback.

in other words I read "son capital" as pertaining to "certification".

HTH