If one borrowed an egg from a neighbor, and found a bloodspot inside, do they have to repay the egg? Should you say that since the neighbor would also throw away the egg if they found a bloodspot then one does not need to replace the egg, or do you say that since you borrowed it then you have to repay it?
The Shevet Halevi, Vol. 10:133, was asked this question and he says that if one buys eggs which turn out to have blood spots it should be considered a מקח טעות (a mistaken purchase), but the custom is not to consider it a מקח טעות because it is impossible to determine the nature of the eggs before they are sold.
And if one borrowed eggs and some of them had blood spots, the lender cannot ask for good ones in place of the bloody ones and it might even be forbidden for the borrower to return the full amount of eggs because of ribbis (interest).