A little. I usually snoop out my vendors and dig up every little thing I can find, every little negative review, etc. I especially look for testimonials from people who have bought what I'm looking at from that exact vendor. The market is big enough and the distro on most things, wide enough that you can do that.
And in general, I find that most internet sellers are on their game. They are big time. The internet is where the money is made. They have the weight to toss at distributors and get the hook-up on resale deals because they can guarantee the sales. Manufacturers generally seem to try and hook up with as many big internet vendors as they can. They want the real thing to be easy to find and purchase online, and most have gotten VERY good at making that a reality.
And on the other side of that, the largest scale productions are the most cloned. They are the things everyone wants to buy. And if you want a clone, you can find it easily. There is enough of a market for them that sellers generally do not see fit to lie about it. You can make really good money just selling clones as clones. They don't have to lie to make their money.
So on one hand, if you want to buy big-name, it will usually be clear whether or not it's a clone. And if you buy small-time brands, you can rest assured that the cloners can't be assed. That's not where the money is for them.
What this means is that you can buy with a reasonable degree of confidence that what you are getting is as advertised... ...if you buy domestically, that is (China really DGAF, though even they know where their bread is buttered.) Most vendors are smart enough to know that the community loves a good witch-burning and will run the reputation of your business into the ground overnight for lesser sins than simply selling clones as authentics.
And yeah, every now and then, clones slip into the authentic market, big time, but on the internet, word travels faster, so the issue is usually put to bed pretty quickly. When clones that even the vendors can't tell are fakes hit the market hard, they usually get found out quickly.
B&M's, not so much. I had been sold a clone or two that were supposed to be authentic. Many times, the people at the counter just don't know, or they are told not to tell you. A lot of these little boutique shops cannot afford to become authorized re-sellers for everything they carry. It costs them significantly more money to stock genuine gear because they buy in lower quantities and sales are limited to a fixed, local demographic. Those are the places where you're going to see clones a-plenty. In literally every B&M I've been in, I have been pitched clones of this and clones of that... ...it's about 50/50 as to whether or not they tell me its a clone off of the bat, though I generally find that if you can show that you know what you're looking at and what you're looking for, they will tell you its a clone when asked.
You really do have to sort of shake it out of them, though. I've gotten into the habit, whenever looking at a display, of asking what are clones and what are not. And sometimes I can see in their faces that they're thinking I'm a dick... ...that I'm basically calling them liars, but at the same time, I have yet to get the "None of them are clones." answer. While not a question that anyone likes asking, it's a legitimate inquiry, as there is a real need for concern.
Semi-related, I was looking at atties in a B&M back when the velocity was just becoming the hot new RDA on the block. I had some store credit to burn through (it was a gift,) so I was shopping for atties. The dude at the counter actually had the nerve to try and pitch me a velocity clone that he said they would be stocking in two weeks. But the thing is... ...even their clones were ridiculously overpriced. At the end of the day, I only bought an atty because it wasn't all my money going into it. I was so amused by this that I ordered the very same clone online for nearly half of the price he gave me and had it in my mailbox a full week before that shop rolled them out.
I just don't know about some of these B&M's... ...I just think that when it comes to clones, they're doing it wrong.