Publishing entities are in too much danger of being sued for plagiarism as is to risk actually committing it. We all find our manuscripts precious. It is often difficult to understand why agents, editors, and publishers don't share our view. This doesn't mean that amateur writers don't face risks in the marketplace. Those who prey upon the unwary and the desperate, however, don't do so by stealing your manuscripts.
Legitimate agents earn their money by selling marketable material to publishers.
Consequently, they don't waste time with material they can't sell. They have no real incentive to market your work, which means you're really no closer to publication after you've paid a reading fee than you were before. As usual, however, if something seems too good to be true, it usually is. They may offer tips and suggestions, but they won't advise you to farm it out for someone else to do the work. Publishers can't afford to hire editors anymore.