A few notes about the bearings listed in the link above.
First off an ABEC rating of 7 isnt the proper bearing to be using in an off road RC for durability. The higher the rating the closer the tolerances are. The higher numbers will damage and wear out much faster then a lower rated unit. Suggested ABEC ratings for Off road use racing and bashing is 1 or at most 3. With such close tolerances as in a 7 a small amount of contamination will cause wearing and failing much quicker. Higher ABEC bearings work well for non contaminating and high speed use. Again, they will offer less drag but you will pay the price in durability and time of use in an off road application.
On a 2nd note, the price for an ABEC-7 of this size direct from the factory in a quantity of 50K units is over double whats being charged by the seller.
The bearings may very well suit the needs of Off road application. My guess is that they are ABEC-1 units being over rated by the seller. There is no way for the buyer to know what the ratings are other then the honesty of the seller. On the other hand, He may just be blowing out old stock for well under cost. I don't want to be accusing anyone of being dishonest. They may very well be as advertised.