Hey @Claude Calixte,
So... let's start with your credit score first.
Everyone knows that we have 3 different credit agency's. What few know is that each of those agency's have multiple scores for each person. I know of at least 5 different levels of scoring. That means, you have at least 15 different possible scores.
Here's what that means... Whoever is pulling your score, requests that score based on the level that want to asses your risk at. Some are going to be more conservative (want a lower score) and some are more aggressive (a higher score). The problem is, even if they tell you what level that they want to pull, as a consumer, you really don't get to see that. If you run out and pull your own score, that agency is going to report it to you based on what they think you want to see. That means that different services may give you different answers as well.
And, if what I just said doesn't confuse you enough, mortgage companies have a unique way of trying to assign you another score called your FICO score. It's really a mathematical blend of scores. And, to make it harder to figure out and understand, it's also possible to pull different FICO's from different reporting agencies.
Let's put this confusing mess into an example...
Lets say you want to buy a new car. But, you're worried about what your score is, so you pull it yourself before you go shopping. When you do, your score comes back at 650. You think to yourself... No problem. I'm above the typical floor of 620. I'll be able to get the financing that I want. so, you head to the dealership and find the car you want. You fill out the 693 pages of loan application paperwork and you're approved. You end up with terms that are way better than you thought you'd get. So, you ask the finance guy at the dealership what your score came in at. He tells you it's 720. You're like... Holy smokes?! how'd that happen? This is exactly what I'm saying above. Yes. You're a 650 in one scenario, but you're a 720 in another.
Here's why I use the car example...
Car finance companies have figured out that people will make their car payment before they'll make their house payment. Because of this, car lenders tend to pick a more aggressive score than a mortgage company would (a mortgage guy might tell you that your score is 622 when you think it's a 650).
Unfortunately, most lenders don't know all of the intricacies of financing either. They just know what they're told. I was in that same boat until just a couple years ago. Someone wanted a loan, I just pulled the report and gave them a quote. I never asked how it all works behind the scenes. I had no reason to question anything. The system worked. But one day I was challenged by a very frustrated borrower. He was very polite and really wanted to know why he was having such a hard time. He gave me the example of how his score was higher when he bought a car and lower when he wanted to buy a house. So, I got curious and started to dig around. BTW... what I said above is not common or easy knowledge to find.
Back to your question as what I think about your deal...
$1,200 divided into $30,000 would be a 4% rate of return on your money. That is not a good rate. There are tons of opportunities that pay way better than that. I've never had a private lender make less than 9% when they lend through me.
IMO, I think you should either go back to the seller and try to negotiate a better deal or move on to another property.
Let me know if you need anything else.
Good luck.