The issue you're going to have it that some of your Prospect Client Name values have more than one "Total value of Potential sale" values. You can sort Prospect Client Name by "Total value of Potential sale" but where there is more than one value, it's going to sum them. If you want to sort by each individual "Total value of Potential sale" value, then bring a copy of that field to the very front of your row column - to the left of Prospect Client Name. Sort it in descending order, and right click on the field, and click "Show Header" to hide it. Now your data will be sorted how you're asking.
Let me know if you have any questions.
In addition to input provided by Paul, here is my approach. You can create a calculation using rank like below:
Replace Sales by your actual measure and convert it to discrete.
Place it in the view and hide header.
Workbook is attached for your reference.
Rank table.twbx 1.2 MB