It's very unlikely you'll get any legal troubles, unless you're a) doing massive volume and b) running offers in niches that the FTC or other government agencies are coming after due to too many complaints (think fake claims related to health / financial offers). But if you are doing massive volume, hire a lawyer to talk you through how you can "tell stories" in an advertisement without breaking laws.
Otherwise, you're biggest problem will be the advertiser not liking it (usually because you're testimonials promise something they don't deliver). But that's unlikely if you know your niche and it helps your conversions back out.
Honestly, neither advertiser or CPA network really cares as long as it backs out, unless the fake testimonials are coming from celebrities / somebody else who can sue. High volume affiliates sometimes get sued by FTC for lying on landing pages, but that's just because the the FTC figures they're an easy target with lots of cash for them to take or they're lying about highly regulated niches like health or financial.
Truth is, nobody really cares if you're deceiving the general public unless you're doing it on such a big and brutal scale that complaints reach a critical mass. It's capitalism.