A custom model can developed from a business's own data on its customers. Information is taken from credit application forms and credit bureau reports. Credit bureau models are developed from information in consumer credit bureau reports. Scores are usually just one of many factors a lender considers in making a decision. This is particularly true in industries like mortgage lending where appraisals and other information play an important part.
Lenders usually calculate application scores directly.
Custom scores can be calculated by lenders or by the credit bureaus with whom they work. This is a difficult question to answer. With most scoring models, the higher the score the better. Higher scores mean lower risk. For other scoring models it's the other way around.