Hi, my name is*****'m a certified appraiser and I'd be happy to help.
The marks you describe are silver plate marks, rather than sterling.
I can date the teapot for you if you are able to get me a clear photo of the mark. Font, placement of letters, etc. all affect the dating of the marks. "Richaud" doesn't come up in any of the marks I've seen, so I'm curious to see it.
I did not receive the photos. I'd be happy to get you more information, but I do need to see those photos. In no way did I say or imply I was done with helping you.
Alternately, I'm happy to request a refund for you if you do not wish to go further.