What if I used sour paint on the walls

Shurline roller covers are a mid range quality cover, but not bad and should do the job fine. I like to use Purdy White Cloud covers for final coats. If you are getting lots of ridge lines, that usually indicates that you are pushing too hard on the roller and trying to stretch the paint. Don't be afraid of loading the roller, obviously, you don't want it to be dripping, but don't work too much out of the roller before you start to apply the paint. If you find yourself pushing harder to transfer color, then you need more paint on the roller. Also do smaller sections at one time, not much more than a 4ft by 4 ft. Cover an area wall to wall one side to the other, then make one continuous long stroke over the entire length softly to even out the paint and remove ridges. Keep in mind, especially with cheap ceiling paints, the first coat always looks spotty and should improve with second coat.

Good question Nick. I manage several rental units and have dealt with the same situations. Originally, flat paints were used in most of the rentals and almost every couple of years they needed repainting especially if kids were in the unit. Flat paint is hard to wash and very susceptible to marring and finger prints etc. The newer flat enamels are better, but not great. I changed over to a harder eggshell finish. Depending on the time a tenant is there, the eggshell really outlasted flat, usually good for 3 to 5 years unless damaged. Satin enamel works great for ceilings, hides marginal imperfections and very easy to clean between tenants. I have also found that since looks is more important than durability, I have used a lot of PVA grade wall paints from Ben Mor. At contractor price, it can be almost half as expensive than premium grade paints, covers well, lasts for several years. I have given up on expecting paints to be show ready after a few years in a rental. Cleaning and touching up walls takes almost as long as painting so a new quick same color wall paint job between tenants freshens up the place and smells new when showing the apartment. I tend to use just a couple of colors for most everything, so I buy 5 gal cans for economy, batch small leftovers and treat older paints with Flotrol. Be sure to keep the color formula in a notebook (ask for an extra sticker) so you can buy a good match later. Changing colors always requires two coats, but one coat of same color is normally fine. You can use your leftovers with new paint if you strain it through a mesh colander and batch it with your new paint, thus slight color changes disappear.