3 bad starters in 2 years

I've got a 1999 Trooper that had it's starter replaced twice, which fixed the starting problems. Now, within 2 years of the first replacement the vehicle is having starting problems and the shop is
saying it is again a bad starter.
My question is What could be causing the starter to go bad so often?
Thank you, Frank
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.