How can I tell if my RAM was tampered with?

Here's the dilemma I went to get my MacBook fixed because the hinge broke. The tech guy also suggested a diagnostic test so I said okay sure why not. But before I sent it in I believe I had a 1Gb ram and still ran my apps/browser smoothly.

So a week later I got my MacBook back and as I tried to use it everything froze. I couldn't even update it to it current state till I restarted the thing. Anyway its updated but everything is still slow & freezing and my RAM is 512mb. So is there anyway I could know if what was removed on my MacBook or should I just take it to another tech?