Differentiating 着 (zhe/zháo) and 着/到
1 - Does 着 have exactly the same meaning as 到 as a result complement?


到 as a result complement indicates the verb is accomplished 

着 as a result complement also indicates the verb is accomplished 

Example:

Both 找到 and 找着 means 'seek' (and found)

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着 as a verb particle is  mostly used to indicate 'the continuation of an action or a state'

Example: 看到 = 'look '(and saw) ; 看着 = 'looking'

着 here is a verb particle that indicates 'continuous state,

Similarly: 想到 = 'think' (and remember or realize); '想着' = 'thinking'

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着 as a verb particle can also means 'result in' 

Example: 买到 = 'buy' (and bought) ; 买着 = 'buy'(and end up with)

着 here is a verb particle that indicates 'result in/ end up with'. As in '买着次貨' (buy and result in buying inferior goods) 

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  2 - How would I be completely sure if 着 would be read zhe or zháo? 


着 read as /zhe5/ only when it is functioning as a verb particle that indicating the continuation of an action or a state

http://www.cantonese.sheik.co.uk/dictionary/characters/1132/