It’s likely a bit of both. Trump has no issue not paying his debts and several entities that have done business with him have gone under because of that.
Russia has to have something on him for him to consider not blowing them off. It’s likely it could be as simple as him considering them a formidable enemy. They could cause problems for him and his family, potentially the foreign assets of his company, etc. They’re not a small bank or drywall company to be messed with.
I agree that the source has bias, but that’s half the problem. Where is coverage from everyone else? If Isreal is not going to open up its detention centers to review or audit, then we have very little to go on and claims like this we have to accept as possibly true.