This is a community help forum -- not an official way to contact Canon for help or guidance (though they do have Canon mods who sometimes chime in).
You mentioned two issues -- which I'll keep separate.
First... you're having focus issues.
I'm not sure if you're using the viewfinder or the live-view to focus but the focus system on the T3i is nearly identical to the T1i in that you have a 9 point AF system (assuming you are using the viewfinder and not live-view) with a center cross-type AF sensor and the periphery are all single-axis AF points.
If you allow the camera to use all 9 AF points the camera is programmed to look for the point which is able to lock focus at the CLOSEST focusing distance. E.g. if an AF point is over some distracting object which is nearer to the camera than your intended subject then the camera will gravitate to that nearer subject. To avoid this, you can force the camera to use the focus point of your choice.
If you are using the viewfinder then the focus sensor live on the floor of the camera. While not common... it is possible that the camera and focus sensors are not callibrated correctly. This can vary by lens. If this is actually the issue then Canon service can correct it, but you would want to caerfully test the focus performance to be sure before going through all the bother to send it in. You need a good high-contrast test target and a non-moving camera. For example... using a tripod to keep the camera steady while shooting a page of newspaper taped to the wall (because the black & white newsprint is a good high-contrast subject) would help you determine if the focus performance is working adequately.
You can also use a focus test chart -- which is even better than the newsprint. I use a commercial chart, but here's one you can download and print yourself ... but be careful to read the instructions to make sure you're doing a valid focus test.
http://regex.info/blog/photo-tech/focus-chart
Second... you're not happy with the look of the images when using flash.
Pop-up flash is good for "fill" lighting but not flattering as a primary (key) light source. In other words... if you're outside shooting a subject on a sunny day in mid-afternoon, you actually SHOULD pop up the flash and force the camera to use it. Set the "Flash Exposure Compensation" adjustment to -1 as a good starting point... this will tell the flash to fire at 50% power. That will result in the outdoor available light being the primary lighting source, but the flash will "fill" in the shadow areas to make weak shadows instead of high constrats / deep shadows.
I have a 5D II and 5D III -- these cameras actually do not have a pop-up flash because it's not considered a very flattering look. To get the best looking results you want to get the flash off the camera and to the side. To have "good light" you need "good shadows" (sort of ironic and yet true.) Also we prefer the transition from light to shadow to be gentle... not a hard, well-defined edge. This is best created by using a broad light source rather than a tight pin-point source of light such as you get with the pop-up flash. When we use a speedlite flash (hot-shoe mounted flash) we try to bounce the flash off a white ceiling or walls and the reflected light creates a very broad light source... a gentle shower of light rather than a harsh pin-point light source.
Tim Campbell
5D III, 5D IV, 60Da
