Fox
lol, I know the waterless periscope cleaner can be a bit expensive these days but perhaps you should of looked for a decent SUBstitute.
Re certificates
I know some certificates can be incorporated into various types of contracts, but this just sounds like the guy wants a commitment from you that he aint paying any more for all the chemicals, bog rolls etc, in this case the word certificate would be wrong, you would need to supply him with a signed suicide note.
For a template try www. kamikaze.com
(just kidding
)