istock.com has been a staple of my design department for years and years, and I must say each year they get worse and worse with their manipulation. I have subscribed, paid as I go and bought signature series. It turns out istock.com has concerned with catch 22's and not stock anymore.
Recently, I purchased $100 in Signature 'subscription' which means that I cannot go back and download past signature purchases unless I subscribe again for images I don't need. This is unlike their credit system in which you can re-download. So stay away from subscriptions, and high-priced Signature collection as you cannot re-download what you paid for.
I hate this company and I'm switching to Adobe stock.
I hope you'll join me and put this greedy, manipulative company out of business. They suck!