I agree with Gacela (pretty name, by the way!)
I'm a professional songwriter and musician ... made a good living at it since the 1960s. And the same is true in mujsic as it is in book writing: sales is no judge or validation of quality. There are songs a fifth-grader could have written that went to number one and made the composer a crap load of money. As a matter of info, a #1 song in the Country and Rock genres will typically yield the composer about $350,00.00 over the first two years (that's when it gets the most airplay and sales).
Same with books, in my opinion. there are so many excellent aspiring authors, many on this site, who can write circles around some of the big-name writers but their book sales yield less than a ransom simply because they've not had the right audience. So, sales and quality have nothing in common.
I wish the gentleman good luck.
Alan