The main reward of this achievement is unique furnishing
And Black Market Mogul is not even close to master angler.

It is a fairly low bar to sell 1 million in stolen goods. I would not think it is a good idea to grant such things for easy achievements.
There maybe a new achievement that could be added that encompasses multiple achievements though most of the achievements are fairly quick to get.
as much as I despise Shads business practices and opinions. . .
. . .I don't mind this one, its very tricky to get, and oblivion had some guild rank names that could work.
prowler, cat burglar, shadowfoot, master thief, etc.

Thestephenmcraeub17_ESO wrote: »The more titles and costumes, the better. Cosmetic diversity is one of my favorite parts of an MMO
I don't think it's any special (anymore). I also got it quite early, when the items sold for half the price they do today, drop rate for blue and purple items was much lower, and Dark Brotherhood as well as Thieves' Guild skill lines didn't exist yet. Getting it nowadays, with all the DB and TG passives, increased item prices and Fence bargaining passives, items that remove bounty on the spot, passives that port you right to the hideout... it's a joke and in no way as much work as Master Fisher. Not even close. Not even 20%.
It's sad they doubled the price on blue and purple items and quadrupled the price on white items (they used to be 10 gold, then 20, now 40) without adjusting the achievement. Add to that the Haggling passive from TG and you've got yourself another random achievement.
But sure, always up for free costumes.