How do other Zenners handle Inventory updates from Vendors?

Good evening... We have been using our Zen-Cart (1.3.8) for about 2-years now and we are continuing to grow in sales and sku's. One of the issues we are running into is managing inventory updates from our suppliers since we do mostly drop-shipping.

I was hoping another zenner(s) could share how they manage drop-ship inventory feeds from vendors. Every vendor is different making it difficult to stay on top of.

Some vendors give us an FTP site to download a CSV file. Others may email us a .txt file. And a third may send us only items out-of-stock.

All the manual work is turning into a full-time job and with us looking to expand to Amazon and other market places we have to be certain our inventory is accurate.

Thanks in advance for any insight or suggestions you can share.

Sean