I recently sold a vehicle while we were in one state and the vehicle was in another. They signed a bill of sale and gave us the money before seeing the vehicle and checking it out. After everything was done I had the original bill of sale and the buyer didn't received a notarized copy of the bill of sale (which they didn't ask for) and is now trying to start issues. The weekend following the sale of the vehicle we traveled to the state and we drove it back to the state in which the sale took place. During which a few issues arose in regards to the vehicle which we were unaware of and the buyer is now upset. We are now awaiting the arrival of the Title from our loan holder and once it gets here we plan on signing it over. Is there anything the buyer can do to stop the complete sign over of the vehicle. If so what can I do to prepare for this? I am making every attempt to get with them to get them a notarized copy due to the negligence on their behalf and nothing can be agreed upon.

Thank you ahead of time!

I'm not sure I fully understand this situation, but I can give you a couple of comments.

1. In your last sentence you indicate "negligence on their behalf". Nothing in your description appears to me to even hint at negligence on their part.
2. I can't imagine why someone (them) would sign a bill of sale and provide payment in full for a vehicle that they haven't seen. But, if you made any misrepresentations about the vehicle to cause that to happen, they may have cause for action against you. Assuming that would have been all verbal - it may be a he said/she said situation.
3. I don't see where them having a notorized copy of the bill of sale is relevant, but I really don't understand why you wouldn't have given them a copy of the bill of sale at the time they gave you the money. Did they actually sign a bill of sale and give you 100% of the money without getting anying to show that they did that?
4. You indicate on the return trip with the vehicle "a few issues arose in regards to the vehicle which we were unaware". That frankly sounds like the condition of the vehicle you delivered to them was different than you represented to them. Your statement that they arose on the return trip, frankly sounds like you may be trying to cover issues that you had prior knowledge of, by claiming they occurred after the sale, but before the delivery.
5. I'm going to make a big leap here and assume that you wrote the bill of sale. If that is true and the bill of sale itself is faulty, any grey area would typically be read in their favor.
6. Given the description that you provided, I think you have some risk should they decide to sue.
7. Beyond legal issues, with your description and trying to read between the lines, it honestly seems that there's something that you have done to take unfair advantage of the buyer. If that is true, I would recommend that you make it right.

They can always sue you, the issue is will they win

What is the "issues" with the car, why are they unhappy

Did you sell the vehicle as-is?

What specific issues are there with the vehicle? Have you gotten price estimates as to what it will cause to fix said vehicle? Are you willing to reduce the sale price because the buyer will now have to pay to have the vehicle repaired?

Also, just signing the title over doesn't do a darned thing. The buyer would have to sign the title and register the vehicle in their name - until they do so, it still legally belongs to you so if it gets towed, guess who's going to be liable?