Hey guys Adulthood here with a quick and profitable guide to 99 thieving. Thieving is very easy to level but can take some time so you have to be patient.
Level 1-50: This is really easy you can steal from 2 stalls these are west of the bank they are called the 'Food' and 'Crafting' stalls.
Level 50-75: from lvls 50-99 you steal from the 3 stalls north of the edge bank. the first first stall you can steal from is the 'General' stall on the far right.
Level 75-90: The next stall is the middle one know as the 'Magic' stall, this will get you all the way up to 90.
Level 90-99: This is the extreme test of patients, this will go slow and you have to keep clicking each time. But it is extremely profitable and you can earn in excess of 20m+.
The 3 stalls north of the bank grant you from 5k to 18k coins per steal which over time leads to a vast amount.
Hope this helped and Good Luck On 99 Thieving :)!