I want to buy a pair of glasses so I can watch the solar eclipse next month. But ideally, I would still be able to watch other things afterwards.
I read an article that said there are a lot of low-quality eclipse-viewing glasses being sold. What should I look for to know I’m getting a adequate pair? What’s a good source to buy from, either locally or online?
These are the ones I got. Made in USA for the reputable telescope manufacturer Celestron, credibly ISO 12312-2:2015(E) certified.
https://www.amazon.com/Celestron-Certified-EclipSmart-Observing-44405/dp/B01N17N0MO/
Just to belabor the obvious, you do not need protection during totality.
If you know a welder, the “lens” from a welder’s mask makes an excellent viewing filter during the partial stage.
Some do, but not all. You need protection from UV and IR as well, and not all welder’s filters do that. Stick with certified solar filters like @wolfpup linked.
The gas place where I get my CO2 canisters filled sells welding supplies. They have a sign they stuck up by the welder’s masks/glasses that says, "WE HAVE NO IDEA IF OUR WELDING MASKS ARE OK FOR LOOKING AT AN ECLIPSE.
Here’s a guide that some might find helpful:
I got a fancier version of these glasses just recently, and yeah, they’re good. Tried them out looking at the sun just before noon one day, and I’m not blind yet.
They’re actually kind of hilarious. When you have them on, the Sun is literally the only thing you can see! 
I used the lens from one with the last partial. It is in my glove box for April.
Warby Parker says that they will be “giving away free, ISO-certified solar eclipse glasses at all our stores from April 1 until the big day (while supplies last).” (Limit of 2 per family)
Before the 2017 eclipse, my eye doctor was giving them out.
Holy crap! When I posted that link just yesterday that set of four glasses was going for $11 and change. Now, 21 hours later, it’s $23.74 for the exact same product.
Thank you, Amazon. No one would ever accuse you of price-gouging! 
Raising your prices may be considered gouging, but it also is a very important economic signal to the market. The seller, by raising his prices, will attract other sellers to the market, which will result in greater supply which will eventually result in lower prices. Otherwise the seller may sell out of his supply and no other sellers may be incentivized to enter the market and then there will be less solar glasses available.
I’d be reluctant to trust any solar glasses that come on the market barely a month ahead of the eclipse, particularly if the maker/seller is largely motivated by the price gouging.
It’s not like there is a huge technical barrier to making these things. 
I believe you meant to say motivated by profit. By far almost all companies that sell things are motivated by profit. Do you avoid purchasing things from for-profit companies? Where do you buy the things you need?
But there were a whole lot of fake ones around the last time there was an eclipse. Any barriers to making the real ones would pretty much have to be higher than making the fake ones.
This also answers your next post: we’ve already seen it happen.
So you assume that any seller in the market attracted to higher prices has to be a seller of fake products. Got it.
Welding lenses come in a variety of strengths, designated by a “shade” number. The lower the shade number, the less filtering you get. Reputable sources including NASA and the National Park Service have indicated that a welding lens rated shade 14 or higher is safe to use for eclipse viewing.
Any business that spends the next four weeks setting up for the production and distribution of eclipse viewing glasses is about to experience a downturn.
So you assume that any seller in the market attracted to higher prices has to be trustworthy. Got it.