I wouldn´t say that it´s normal, but unfortunately there are, in fact, a lot of people who aren´t really able to deliver good quality - but as you already noticed, you can often tell that by the way they reply to your BR. Look at their profiles and gigs for further hints, or, if something seems off, you could message them, ask some things about their gig, or questions that will tell you, if they understand what kind of job you want them to do for you, that more or less live communication has the least chance of being ‘faked’ (sadly some people do steal gig descriptions, profiles, even portfolios from other sellers, so their profiles and descriptions etc. might tip you off, but not necessarily so).
You might have better results, if you don´t rely on Buyer Request posts, but ‘actively’ look for sellers who offer what you need, many sellers don´t even look at the Buyer Requests (partly because they are good enough that they get enough orders already, partly because the Buyer Request section, alas, gets spammed a lot by the kind of sellers who don´t understand English enough to be aware that they aren´t supposed to post in there, and that only other sellers will read their ads, and it´s too tedious to scroll through all those misplaced posts to find the genuine Buyer Requests).
Of course, the language abilities of sellers won´t matter (that much) in certain categories (though it´s always a plus if you can communicate well enough to avoid misunderstandings and such as much as possible), but, yeah, for translating or writing gigs they usually will matter.
Good thing that you can detect a lack of ability to write correct English quite easily, it´s more difficult for buyers who want a translation into a language they don´t speak/read themselves, I got a couple buyers who bought from some scammy sellers first and ended up with Googe Translate texts, so they didn´t win anything by paying a low price (at least I hope they payed a lower price for that! lol), but rather lost money and time.
Investing a bit of time (choose your seller wisely) and a bit more money (maybe there´s something wrong with the gig 'I translate into all languages in 24 hours 1000 words for 5$) upfront often will pay off for a buyer,
the prices here on fiverr are already much lower in most if not all cases anyway,
than those you´d pay elsewhere for comparable quality, so I´d suggest to not make the price your primary criterion in choosing a seller. Good quality for a fair price should make you more money ultimately, than bad quality for a too good to be true price.
Buyers who are willing to pay fair prices, as you seem to be :), can find good and even great sellers here for all their needs, the art of the fiverr game is to sort the wheat from the chaff, an art which is important for both buyers and sellers btw.
Anyhow, welcome to fiverr, and you´ll surely find some great writers for your project, I know for sure they exist, some of them even write on the forum regularly, so maybe look there, you´ll recognize them by their great English, good grammar and engaging way of writing, if you won´t find any through Buyers Request, or else use search with the relevant keywords for your purpose, good luck and success with your zen centre!