Ok, now i've got it...
When i ordered your product 3 from the Settings sapmple csv, for product with ID 38, inserted this into the post meta:
(138, 38, '_price', '200'),
(139, 38, '_regular_price', '200'),
(140, 38, '_sale_price', '190'),
When i save the product, the new meta will be this:
(138, 38, '_price', '190'),
(139, 38, '_regular_price', '200'),
(140, 38, '_sale_price', '190'),
So as i see, regular_price stores the original price of the product, sale price is store the sale price, and _price strores the price to show.
And, the price is for sale only, if the _price and _sale_price are equals.
So if you overwrite the _price with 170 in the db, on the page, 170 will appear, but not as a sale price.
Hope it helps to fix this.