drag=sticking point for the deal

I read this as being about the time delay between the reloc company buying the house and reselling it. During that time their money is tied up in the property and they take the risk that the house might not sell, either at all or at their valuation price. They are probably incurring loan charges etc. They make their money from their initial fee for valuation + their 3% to 5% difference between the price they buy for and the price they expect to sell for (their valuation) + any extra profit if they are able to sell at a higher price. Perhaps they pitch their valuation deliberately low to increase the chances of the property selling within the 90 days and, in the event that it doesn't, to also increase their chances of selling at a higher price.