We do guarantee delivery on everything we sell.
We must tell you though that we cannot 'control' nor 'push' the US Postal Service to deliver faster. Nor can we contact foreign governments and ask for an item to be searched for. To that extent, once it is mailed, both The DNA Store and you, must rely upon national and local postal services for deliver.
Often regular postage overseas (we are in the USA) can take 2 to 6 weeks for delivery.
We have found that Fed Ex, while expensive, is very reliable for service. If you need it fast, this might be a good option.
Bottom line, you will select the shipping option which best suits your situation.