I would never accept a patch job on a tub. I'm not a contractor nor a builder, but I think it's pretty obvious that the tub has to be replaced and the sub floor problem dealt with. Forget about dealing with the realtor, he just wants to close the deal so he's playing both sides. Have a licensed contractor examine the situation. My bet is he will give you about the same advice. If you accept this shady deal, you will be stuck 100% for the eventual replacement and repairs. Might not hurt to consult an attorney either. I really think you're being flim-flamed.