There is this .com domain I want to registerer (expired domain) the .net is been used by a big company with content on the .net,but not their main site should I go ahead and reg it, can I flip the .com with this company please advice
Considering it's not their main site, there's 50/50 chance they would be interested with the domain. If there's no trademark, it's worth a try. You can use a promo/coupon to minimize your lose.
If there is no trademark, why not. But always keep in mind that you rarely should reg/buy domains when there is probably only 1 potential buyer. And as mentioned, you may use a coupon for this one.
If you using a coupon and price the domain reasonably then u might score....maybe drop in a one liner in ur email about it's a good thing u managed to grab the domain name bcause there would have been nothing stopping their competitors from grabbing the domain name and redirecting it to one of their own sites.