I get offers all the time. Since 1/1/13 on one well where I have a 1.04% Royalty I have received in excess of 34 offers with the lowest being $12K and the highest being $125k. They are buying everything you own in that county, both producing and non producing. this will kill the goose that lays the golden egg.
A friend of mine who owns one of those companies who is always filling your mail box, confided to me that they had a minimum profit of 25% day one but often times quite a bit more.
I would make sure that this is what you want to do before you sign that.
Also, it could be that the lease is holding far more acreage than what is being used in production and are you being fairly compensated for that for which production is not currently taking place.
I would sleep on this decision, and maybe ponder it for years to come...in other words, no thanks.