DIY needed for amplifier for sedan install

[YarisSedan]

So I am tired of taking my car to places to get things done and having crappy service and low quality work.

I am wondering how hard it is to install a amplifier to the factory intergrated deck. I have seen people install them with no problems. I dont mind paying someone but afraid of a hack job. If anyonie has read my other post about what best buy did. I am afraid to take my car to another stereo shop now.

I plan to mount it under the passanger seat. Not really sure which wires go where and how to wire the wires where to keep everything nice and hidden. I have mechanical aplitude so removing stuff is not a problem. Just all the electrical wiring and where everything goes. Unless someone in the bay area i can trust wants to do this for me theres a 100 bucks in it for you =).