Too trusting (5)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">too trusting</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for naive that I've seen before include "Simple, innocent or unsophisticated" , "Artless, innocent" , "Gullible, too trusting" , "Ingenuous, easily deceived" , "Ingenuous and credulous" .)