I'd decline the CC charges and state why. Sounds way too shady to me.
I just had my Indy rebuild my transmission in my 560SEC and it was just a bit less than the $1800.00 in your quote and I trust my Indy as does anyone else that uses him in So.CA.
I had estimates from 600.00 to remove and reinstall the tranny. plus $2300.00 to do the rebuild. I passed. I also had one estimate of approx 800.00 for the whole job. I thought it was too cheap and I passed. Glad I let my Indy do it. it is as perfect as I could ask for.

Bottom line, you get what you pay for.

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1986 Euro 500SEC "RUF" 9:1CR, "Rose"
1985 Euro 500SEC Cabriolet AMG Widebody
1982 Euro 500SEL "Blue"
2001 Texas Heeler (Aussie/Queensland X) "Sulphie",
2012 Queensland Red Heeler "Squeak"
Best dogs I've ever had.