Impact of dropping a phone?

The first time I cracked my phone screen I ignored the crack but after a few weeks the phone stopped working -- couldn't turn on even after factory reset/charging/etc. Brought it to the store and they said that I had dropped my phone so hard that the internal parts became loose and couldn't work properly anymore. Sounded tacky but I just believed them and got the screen fixed, as well as some parts inside.

I just went out for a skate and stupidly enough I was holding my phone in my hand -- I hit a small rise in the concrete and my phone flew out of my hand and hit the ground pretty hard. Checked my phone screen and sure enough, another huge crack.

Question is, is what the guy said at the store true, that you can spoil your internal parts from impact?

And if it's true, is it possible to tell by any means, before the phone stops working after a few weeks -- just like the last time round?

I'm asking this because I really don't want to waste money repairing the screen anymore, but if the internal parts are messed up then I have to send it in for repair anyway, so better soon than later. (right?)

Thanks in advance guys.