I Think there is a difference between the s sound in ψ and the single s sound of σ (and ς): the first is a Clean s, the second is Close to English sh (or s in Madrid Spanish). If I had thought of this difference, I could have avoided guessing that what I Heard was σάρι. -- Peculiar autocorrect here - it changed my t to T in Think, c to C in Clean and Close, h to H in Heard. Similar things have happened Before.
The 1st person singular of the verb always ends in -ω, e.g. παίζω or μπορώ.
For masculine and neuter nouns and adjectives, it will always be -ο.
For feminine nouns, it can be either (but both are very rare). If the word ends in -ος in the nominative, it will end in -ο in the accusative, e.g. οδό. But if it ends in an O sound in the nominative, it will be spelled -ω, but these are usually names like Βάσσω.