I worked in a web shop which had to produce spreadsheets which people wanted to look at in Excel. I gave them so many options, and told each client to experimen

I worked in a web shop which had to produce spreadsheets which people wanted to look at in Excel. I gave them so many options, and told each client to experiment and choose the option which worked for them. In the end, we had (a) UTF-8 CSV, (b) UTF-8 CSV with BOM, (c) UTF-16 TSV, (d) UTF-8 HTML table with a .xlsx file extension and a lying Content-Type header which claimed it was an Excel spreadsheet. Option a worked fine so long as none of the names in the spreadsheet had any non-ASCII characters. Option d was by some measures the worst (and was definitely the largest file size), but it did seem to consistently work in Excel and Libre Office. In fact, they all worked without any issue in Libre Office.