If you need 99%+ accuracy go for AWS Mechanical Turk. They are used by Wave Accounting and other office application companies for receipt OCR. For 85-95%+ accuracy any off the shelf solution like Google Cloud ML APIs or AWS textract will be fine. You can get better results with both the cloud APIs and hand rolled ML models if you have a good dataset. For this sort of applications a large quantity of well annotated data is king. If you only have <100 receipts per year and need very high accuracy it might be cheaper to just go with AWS Mechanical Turk end-to-end. You have to pay people to annotate the data anyways if you want to train a model so it might be easier to just stick with humans.