Manufacturers make optics to make money and their business won't last long without a solid product. Because of this most conduct pretty thorough testing before their optics hit the market, and they provide good company support for any problems or questions you may have. If you want to know how loyal a company is to its product, just look at the warranty. Some of the best include a lifetime warranty where, aside from running over your optic with a tank, they'll repair or replace it at no cost to you. Remember, the money you pay for an optic isn't only for the initial product, but for the support and peace of mind you'll have for that investment 10 years down the road. The price tag shouldn't be anywhere near the top of your priority list.
I would also encourage researching the testing other agencies and end-users have done on that particular optic. The military is likely the most thorough when it comes to testing optics, or any piece of gear for that matter. Their motivation is simple; if the military gives it to their troops, failure isn't an option. The U.S. government has an almost unlimited budget for this testing process and if you've ever reviewed their findings you know "thorough" doesn't begin to describe their methods. If an optic has earned a military specification number, you can be pretty sure it is a solid piece of equipment.
If your agency is like mine, you have neighboring agencies and jurisdictions you work with daily. A simple phone call to their firearms staff can provide a lot of good information.
I am fortunate to work in a large metropolitan area with many different agencies to collaborate with. Every year we make a point to get together for a few days of training and sharing of ideas. You'd be amazed how much can be learned from only a few days of talking to your peers. If you or your agency doesn't normally do something like this I would strongly suggest you start. On more than one occasion I have considered a piece of gear or tactic only to find out another agency has already found it to be unreliable or ineffective.
Most importantly, once you've weeded through all of the research and testing and decided on an optic that is right for you or your agency, you must dedicate the time and training necessary to utilize this tool properly. The best equipped, most advanced, and insanely expensive weapon system in the world is worthless in the hands of an untrained operator.