Legal advice: in this case, there has to be evidence of the advance money of 5000 which Bill had paid to Tom earlier. The lawyer will ask for that evidence Moreover, it was a verbal agreement between Tom and bill that Tom would sell his business for 50000, However, there was no receding or proof of such an agreement being made. This case is a breach of contract or proof of such an agreement being made. Thai case is a breach of contract however, it needs to be supported with concrete evidence.
Bill must have taken a receipt from Tom of his paying of 5000 or Tom must have given something in writing to Bill as a proof of receiving of 5000 from, Bill which would serve as a token advance to book the business and later to pay the remaining 45000 and buy the business.