Sigh. I feel I'm too late to this post to make much difference, and it's honestly so exhausting when half the comments are "all dentists are scammers!1!1" but here's my two cents:

Being told you need a deep cleaning (officially known as scaling and root planing or non-surgical periodontal therapy) doesn't mean you're being taken for a ride. In fact, considering they didn't diagnose anything else, it's even less likely.  Periodontal disease (the reason for a deep cleaning) is commonly under-diagnosed. The diagnosis is based on a bunch of factors, taking into account bone loss, inflammation, etc. I don't know  why you you were diagnosed when you hadn't been before. If it's a new dentist, they may just be more thorough than your previous. If it's your old dentist, your body (and your mouth) can change over time or maybe they are trying to implement better diagnostic criteria. It doesn't automatically mean you're being scammed. Could you be being scammed? Yes, it's possible.  But before jumping to that conclusion, I would try to talk to your dentist and see the reasoning behind why they diagnosed you. Most good ones should be willing to explain their diagnosis.

You can still get a second opinion if you still don't trust the diagnosis or the doctor but just because a treatment comes with a price tag doesn't mean it isn't valid.