English is not my native one, but I can talk and write with it, but maybe not as well as I would like to. Many readers have told me that my stories I wrote are really good, but still, I make some grammar errors. Yes, I could get an editor, but I can't do that yet (financial problems). Somebody told me, publishers edit every manuscript anyway (or maybe is that wrong?), so what are my chances to get my manuscript to accepted by publisher or agents?
No one will reject your manuscript because of one or two typos. But, yes, it needs to be in correct English (or whatever language you're using) with very few mistakes. This applies to your cover letters and other documents too.
If you can't afford a professional editor, try to find one who will barter with you. Maybe you have a skill that person needs.
If you can't get a professional, find at least one native speaker of English to read it for you. If they use paper, hand them a red pen and insist that they circle everything that is wrong (and fix what they can). Do something similar for computer editing (for example, changing the font to red). Avoid people who are super nice, to the point that they won't tell you if you made a mistake. And make sure it's someone who writes well in English and understands grammar.
You'll use a spellchecker of course but an awful lot of wrong words are spelled correctly. You need a native eye to catch most of those.
When I've read articles about submitting manuscripts, the number one thing most of them talk about is to fix all your mistakes. Something littered with errors is not going to look good. It is likely the reader won't even get past the first chapter.
As a note, your question has one outright grammatical error (huge one) and at least two other spots where the language is technically correct but a bit off from how a native speaker would phrase it. I'm not going to avoid answering your question because of those errors, but I wouldn't read a whole novel like that (even a draft), unless my job was to fix it.
I'm a native speaker of English and, when I submit my own novel, I'm going to have several people read it to catch typos and other mistakes. It's hard to edit your own work, even if your language skills are good enough to edit other people's (which I have done).
From what I understand, a few errors usually won't be the main cause for rejection. If there are a very large number of grammatical errors, or a fair number of glaring errors, that might tilt things towards rejection. But then it depends on how good the writing is. In other words, I'd want to submit something that was "good, but not necessarily perfect" on grammar. (Of course, this doesn't apply to intentional violations of grammatical rules as a matter of style.)
Very likely a rejection. I have a book written by an agent that interviews dozens of other agents, the bottom line is that agents are looking for a reason to say NO, because they have 50 queries for every query they could afford to take.
I suggest you use a spellchecker, #1, and do not ignore ANY flags.
I suggest you get "grammarly" (just google that word), a package that you can get for free to check basic grammar, and pay some more (but it is far cheaper than hiring a person) for more advanced features. Like suggestions for rearranging sentences to be grammatical. They advertise it as a "Free writing assistant".
Agents do not like submissions that need work to read well. They don't mind colloquial English, they won't be deterred by a split infinitive or ending a sentence with a preposition, especially if it is in dialogue (people are not grammatically correct in their speech), but even in prose if it sounds right they will let it slide. But they don't want to do the work, and many are not "editorial" agents willing to do that work, so they reject it.
And usually if you are rejected by an agent, unless she specifically invites you to fix the errors and resubmit, you should not submit the same work to her again. (85% of agents are female, by the way).
Take advantage of what is free out there, or buy a package to help you. The way the agent sees it, when working through her slush pile (queries), she has to reject 98% of them, and the faster she does the quicker she gets to the 2% that looks and sounds great. She has zero incentive to give you the benefit of the doubt, and if you can't even use the free tools at your disposal, she will see you as not serious about your writing, and not someone she wants to work with. She is there to make money, and extra work for her means fewer dollars per hour of work for her.
She cannot see your work as having "potential" if she just works with you, because she cannot possibly do that for the other 49 out of 50 queries she is going to reject this week, and has no reason to single you out for special treatment.
Get both your spelling and your grammar in order first; for your query, your synopsis, and throughout your book.
The publishing industry has become extremely competitive in recent years. The effect is that publishers only invest money in extensive editing and revising if they are absolutely sure that the book will sell millions. And that is the case only in established authors or in clones of current trends.
If you fall into either of these categories, grammatical errors won't matter. But if you are a first author and you haven't written the next 50 Shades of Grey, then you'd do better to show your professionalism by submitting a ready-to-publish text.
For the agents--You will only need a perfect query letter and opening pages. If you find an agent that requests the full manuscript, you can explain your situation. If they find your story compelling, I believe they will work with you.
So, my best answer is that some errors is not ideal, but also not a deal breaker. I'd say be sure to get your query letter and opening pages in perfect shape. Perfect.
Be aware that only about 2% of queried manuscripts find an agent.