One has to read: ביציאתה “at her exit” instead of במציאתה “on the occasion of her finding.”
This is the text of the parallel in Bikkurim. Text here: שאין אדם “for no person”.
It seems that one has to read בְּעָרִיס (this is the word translated).
This sentence has several corrections in the ms. It seems that the scribe first wrote שֶׁאִין עָבַד הַגִּזְבָּר וְתָפַס אֵין מוֹצִיאִין מִיָּדוֹ “if the administrator acted and took it, one does not take it from him.” This is a correct sentence but unvocalized it is misleading because of the simultaneous use of Aramaic אין “if” and Hebrew אין “not”. Therefore, the scribe crossed out the first אין and replaced it by לו, read לוּ “if” which the corrector then completed (somewhat redundantly) to אִילּוּ. The scribe also changed עבד “acted” to עבד “acted wrongly” and crossed out (mistakenly) the second אין. The best version is the original text.