It is an interesting process. When I came back to shopping more than a decade ago this forum did not exist but other forums did. I spent a lot of time reading there. I found that when I googled the name of one company I could sometimes find a list of companies that someone had posted on the internet. Some of those lists were obviously very old. There were lists that included the street address to write to the company to join, lists that included website addresses and lists that included clients and/or types of shops performed. My policy was to register with any company I found. If I was accepted as a shopper, the chances were good that the company was still alive. Many many companies I never heard back from nor did I get an acknowledgment of receipt of application.
Where possible, I did a first job for each company to test the waters unless I had found excessive comments on forums regarding non-payment. As I'm sure folks have noticed, shoppers differ wildly in whether they think a company is good or bad when they talk about quality of instructions, of the shop, of the payment and of the editing. What works for me may not work for you and vice versa. The critical bottom line to me in judging the health of a company is whether they pay as agreed, when agreed or before. If a company states 3 months to pay and they pay in 3 months or sooner, that is fine because they are upholding their end of the contract. If I didn't know that it would be 3 months when I contracted with them, shame on me because I failed to do my homework. If they take 3 1/2 to 4 months to pay when we contracted for 3, shame on them.
I have done some completely stinko jobs for not much money, but they only got my services once. While some of these companies have fallen by the wayside, others still exist and still get 'bad press' from shoppers as being cheap, stinko jobs. Over time my shopping has evolved to working primarily with companies that pay reasonably without having to slap on bonuses to get the shop up close to what it should have been paying in the first place. I appreciate their professionalism. That doesn't mean that I never get bonuses from them, but those bonused shops are generally because some other shopper flaked and they knew I wouldn't or it was a shop that the content did not interest me, but the hefty bonus did.