Hi Jessica! As Martin says, the main thing is to choose a reputable company. If you share who you are looking to buy from, forum members might be able to comment on their experience with the seller.
I bought our house on pay monthly with Bulgaria Direct, so I can only comment on their process. Other sellers might do things differently.
It's not a mortgage, more a rent to buy scheme. They own the properties they sell, so they are the seller, not an agent. Mowlem, another long-established seller, works the same. The buyer gets the right to use the property but doesn't actually own it until the payment is made in full. There's no interest, because it's not a loan, but the asking price may be a little more than actual market value to cover admin fees.
When the deposit is paid, that starts the process and you're committed to buy. They'll ask for things like your passport information, UK address, etc, so they can prepare the contract, which will be posted to you. It's in both English and Bulgarian, and seemed legally correct to me. Obviously it's under Bulgarian law, not UK law. If you're happy with the contract, you sign it and send it back.
One thing to be very aware of that's stated in the contract is that if you fail to make the monthly payments, all rights to the property revert to them and the buyer loses whatever they've already paid. Only start a pay-monthly purchase if you are sure you'll be able to continue making the payments.
Any time after the contract is done, you can get the keys and start using the house, including renovating it. Unless you're very experienced with Bulgarian village houses or buy a more expensive fully renovated property, chances are it will be in worse condition than expected and need more work than you thought it would, so be ready for that. I thought I knew what to expect. I was wrong! I love my house and have no regrets, but I did cry my first night here when I discovered the amount of fixing-up the old place needed. You also take full responsibility for all bills associated with the house from the date of contract, things like council tax, electricity, water.聽 They sent invoices for these.
Once the house is paid off in full, they'll arrange the legal transfer of ownership. This happens at the local notary's office in Bulgaria. Unless you have EU citizenship, you need a Bulgarian company set up and the company buys the property, as non-EU citizens can't own land. Bulgaria Direct helped with that. There was a fee for this, which was clearly stated in the documents sent with the contract.
I found Bulgaria Direct excellent to deal with. There were no hidden fees, no dodginess. The only issue was the misunderstanding about one aspect of the house condition.
I would suggest if you haven't been to Bulgaria before, come and have a look first. It's very different to the UK and Western European countries. People tend to either love it or hate it.
I hope that helps and good luck with your Bulgarian adventure!
