I understand were your coming from. You have a few options- ignore them, turn the chat off or engage them with humour. One thing is most are ok, some just want attention and not everyone can pay. If you engage in chat and don't come off as aggressive you'll find most are engaging. Never dismiss anyone, you never know who the next big tipper will be. Gray one day coloured the next.
Hope that helps.
Welcome, Have fun and be lucky.

I always talk to them as I know not everyone has got money to spend on a cam show and as long as I put on a good show I hope that they will follow me and come back and that when they can afford to give a tip they will and it could be a big one

Hi and welcome to cam101 x

This is easy, firstly some sites have filters that you control to admit, or allow greys to chat, if they are there then you can use them.
On the other hand, it's your room, your show, your rules, anyone who causes issues can be warned, silenced or banned.
Personally I like to have greys in there as it raises the viewer count and moves me further up the ranking on the site, however, they don't get away with much.
They get asked politely to behave, then told, then dealt with.
Once the other greys see that, they tend to behave better.