The last time I heard places like Brandsmart did free radio installs if the radio was more than certain amount of money. Him installing the radio would not void any warranties. The warranties are with the make, not the store. The store has to follow the warranty of the make. And since he will have to pull the radio out to hook up the amp, its pretty much just worth for him to do it himself anyways, so theres less chance of screwing up anything when he pulls the radio back out, specially since unless he purchased a wire harness as well, some places might do crappy wiring jobs.