It is often hard to convince or show a client that what you are doing is improving things. In my opinion, CPA is the bottom line metric. Some get it - eventually - some never do as they look at another number.
As an example, client did their own PPC. Their hire you thinking an expert should do better. But what they look at is the 200 sales they make from PPC last month. Problem is, their campaign was not very targeted and the CPA is $40. You come in and the CPA is down to $20 although there is only 100 sales. You need to make them understand this is better because they were losing money with poorly targeted keywords. The other 100 sales they were making were at $60 each. Some insist, at first, they want you to maintain and increase those 200 sales. This is an extreme example but is the kind of thing you can run into.
In my view, reports regurgitating a bunch of numbers from accounts will only confuse them and shows no value. Typically, less is more. Do show before and after results and why they are good/bad. Make recommendations above and beyond just the PPC management such as SEO and landing pages to help improve conversions.
One client I have wants to know each week "how did we do"? It's always revolves around the conversion rate and CPA. So I tell him, one paragraph, that the 7% rate this week at $8 was slightly lower than the previous but the same week last year it was only 5% at $10 so obviously there's been improvement. Nothing fancy in his case. Last month, the week was poor, no explanation as to why. Digging deeper, there was three days the rate was much lower than normal. The rates can fluctuate but not by less than half three days in a row. Armed with this, he'll see if the culprit was the hosting service or checkout software and if he can get some kind of refund.
Another new client, I did extensive research into his account data. I found out that his campaign did very well prior to two years ago on conversions. The only reason I could figure out is that he changed landing pages which did better at converting. There's no reason why my ads would do twice as bad for the same keywords as his two years ago. He said there was a change about two years ago and will reuse those landing pages. He never realized his new pages were detrimental to converting. Result: happy client.