You could use Google Ads RLSA (remarketing lists for search ads) to do a negative bid adjustment on recent customers so your ad is less likely to show up. Essentially you would just upload a list of your recent customers to a shared library audience, add it to your campaign(s), and then set your negative bid adjustment.
We also use RLSA to target our less recent customers who might be in the market to buy again and do a positive bid adjustment to make sure we turn them into a repeat customer and don't lose out to a competitor.