Is it common for seller to not provide tax returns for property?

[Rich Somers]

My lender asked for seller to provide tax returns for the past 3 years of a 5 unit i have under contract, and seller said no. My lender said it’s fine but it limits the number of banks that would be willing to lend to me which could result in less than favorable rates and terms. Is this common for “mom and pop” type owners to not be willing to provide tax returns for a property? Also, seller provided copies of signed lease agreements..but in addition to this would it be a good idea to request estoppel agreements from the tenants?

Thanks!