Sens bon

If that English phrase has 2 or more meanings to you, then only context will allow a distinction. That holds true for any language. In speech, there may be additional clues from intonation or emphasis etc

Using ‘I smell good/bad…’ in English refers/should refer to the perceived quality of one’s own scent or odour. This is what ‘Je sens bon/mauvais’ translates to from French.

In English, it is or should be  ‘I smell well/badly’ or ‘I have a good/bad sense of smell’ to refer to sense of smell.

In French ‘odorat’ is the noun for sense of smell, so ‘J’ai un bon/mauvais odorat’ specifically refers to one’s sense of smell. 

In neither English nor French need there be any confusion between describing how well your sense of smell functions, as opposed to what sort of smell you release ! 

In the lesson link attached below, the first section descriptor should be changed, as sentir does not actually mean (express) ‘the sense of smell’, but it does mean/express ‘the perception of smell’. 

Sentir can also refer to ‘the perception of flavour/taste’ - however  ‘the sense of taste’  is ‘gout’ - ‘J’ai un bon/mauvais goût’.

(There is a difference between ‘the sense’ and ‘the sensation’).

 It may be worth noting the specific words for the senses in at least one of these lessons on sentir, as well. 

Describing senses with "sentir" - The different meanings of the verb "sentir" in French 

https://www.larousse.fr/dictionnaires/francais/goût/37667

https://www.larousse.fr/dictionnaires/francais/odorat/55620

Thank you.