>「信用{しんよう}ほど、積{つ}み上{あ}げるのに苦労{くろう}して、失{うしな}う時{とき}が一瞬{いっしゅん}なんて、割{わり}の合{あ}わない投資{とうし}はない。」

The core of the sentence is:

>「信用ほど割の合わない投資はない。」

The entire middle part 「積み上げるのに苦労して、失う時が一瞬なんて」 just adds more information to the core.  **It would not change the basic meaning of the sentence one bit**.

So, let us examine the core now.  Notice that ほど is paired up with ない.  The core says:

>"There is no 投資 as 割の合わない as 信用."

>= "There is no investment as not-worth-the-candle as trust." 

In other words, it is saying that trust can be really rip-offy.  But why, you wonder.  That is where the middle part comes in telling us how it can be so rip-offy.

>「積み上げるのに苦労して、失う時が一瞬なんて」

>"(as/because) one struggles much to build up (trust) yet one can lose it in a flash"

I hope I don't have to combine the two parts into one English sentence.  I shall leave it to you as it is your language, not mine.