S30.World I wouldn’t give it another thought. Many folks on this site have purchased tanks from them including myself and were very satisfied.

Submerge the sending unit in CLR (calcium, lime, and rust) for 24 - 48 hrs. It will come out clean and usable.

You can also bench test it before you reinstall it. Quite a few articles here on the site referencing that.

I've done two tanks and it's not hard. You have to get everything together and plan it out as things have to be done pretty quick. 10 years ago it was $50 for all the chemicals. The only thing is letting it cure for about a month, most important. So if your in hurry to get on the road buy a new one. If not clean and coat it yourself.

A gallon of acid, $5, couple boxes of baking soda, $5, gallon of acetone $10, quart of red-kote $30. Plenty of empty 5 gallon buckets and a leaf blower.

I borrowed ideas from these two guys and added a few of my own from past motorcycle tank plus the instructions from Red-Kote.

https://atlanticz.ca/zclub/techtips/fuel/gastank/index.htm

https://woodworkerb.com/home/datsun-240z-rebuild/240z-fuel-tank/

https://www.damonq.com/techsheets/red-kote.pdf

What would you say the success rate is. I’ve seen both results reported here. The overall condition of the tank is probably going to be the deciding factor. I had my tank redone at a shop, keep in mind you’re at their mercy as far as the job you get. At the end of the day my tank began to leak from minuscule rust pit holes. That’s when I decided to purchase a new tank. Again it’s all about what shape your tank is in and you really won’t know until you remove it.