The author gave valid reasons. One was a wrong assumption about the input files and it looks like the author was willing to absorb that. Then more changes were

The author gave valid reasons. One was a wrong assumption about the input files and it looks like the author was willing to absorb that. Then more changes were asked by the client. Small fixed priced contracts are hard and limiting liability is critical. Typical is limiting it to value of contract. Otherwise it is very limited upside and unlimited downside. Key to make it work is change management but that assumes reasonable people on both sides and getting started with it early on.