Pathological liar

Son-in-law is a pathological liar. My SIL tells liar after liar, I don’t know if it is a medical condition or not but if one Police car went past him with blue flashing lights he would tell others it was ten police cars. He told me that they can not afford a window cleaner because he is too expensive at £25 “ just to clean the fronts” . We have the same window cleaner we live eight doors away from SIL same style house
Window cleaner cost us £5 to clean the front £10 all the house. He told my daughter that a fencing contractor had told him the cost to repair their back garden fence would be £3000. One week later the contractor telephoned to ask if they wanted the work done, my daughter took the call she told the man he was far too expensive. He replied “£250 is a fair price”. There are numerous other times every day SIL tells blatant liars. I despair of what he will say next. Any ideas on how to deal with this.