This whole questions is double-sided.
At a gym like 24 Hour Fitness, the "trainer" is expected to "recommend" a certain level of supplements (nutrition stuff) to the "client." Some of the trainers are exceptionally clueless, and it's a numbers game. Some are qualified, but have to make a living, so they still succumbs to the pressures of a gym like that. I.e., you don't get what's in your best interest, but, rather what has higher margins.
Other gyms, like LA Fitness, have their trainers on a hourly basis, without incentive tied to "supplement" sales. That's certainly more ethically, but, you still can run into clueless trainers.
Now, here's something you should know...especially if you are looking for excuses on why you failed: 1. 120 at 5'8" isn't petite, it's starving. 2. No one at the gym gives a rat's tiny behind what you look like. Many experienced lifters are more than happy to help a newbie, if you don't come off as a complete low esteem loser. 3. It's not rocket science. Watch others that are good at it and use common sense. 4. Nobody said it wouldn't be hard from time to time (e.g. competitive bodybuilding), but, in general, it should make you feel good and isn't all that hard. It's a lifestyle. 5. You can't make gains if you are anorexic, and can't or won't eat. Nutrition is so very much part of sports science, and, believe me, it IS science. 6. Learn about pain. There's good pain, telling you that you worked a muscle / trained hard, and that's bad pain. There's a fine line. If you want to make gains, likely there will be some pain involved the way. In can guide you in your training effort and keep you from making bad judgments.
I have been lifting for 31 years. I've also studied my craft, at great length. I don't like training people because most refuse to set themselves up for success. If you hire a trainer, dont' make them a crutch for your own insecurity. Give yourself permission to like yourself, and things will come together. I have two trainers (Sagi Kalev - on the cover of Muscle and Fitness more than any man alive - http://www.sagikalev.com, and Jesse Levya - Texas State Champion Middleweight - http://www.txsportsclub.com) and they are extreme valuable in my training. They pick up on things I missed, and are constantly giving me sound advice.
Here's me...in all my glory...http://www.bodybuilders.com/chuckg.htm.
Set a goal; come up with a plan for success; train smart; have a good work ethic; eat; study; rest; ask folks; come to like yourself..and finally, learn patience and diligence. And...PICK UP YOUR WEIGHTS...
Like I said, most big guys / fit guys are happy to mentor others if you don't turn them off with extremely low esteem.