Thank you for concerns and suggestions.
Deletion will not be possible as of now. Will work on some solution. Instead of delete will have option to hide unused products and customers.
Regarding Receipt and Payments, yes agreed it needs some immediate changes. Will make a video on how to use Receipts and payments options.
Further if any mistake is made, there is no option to correct it. Even I am suffering with it :)
By this weekend will code and release a dashboard for payments and receipts which can be edited and deleted.