Well since he doesn't want to build, he can get the i7-2600...however he is risking warranty. Spending that much money on a build can cause issues. Like, is the PSU still good? Has the previous owner attmepted to overclock the CPU shortening the life of the CPU? There are plenty of reasons.
It also depends on what your friend is planning to play. If he is just wanting to play simple games, then I would strong suggest building it with a G4560 and upgrading later. If he wants high end games, he may need to consider the i7 and a GTX 1060. However, with the mining craze, it's hard to justify a budget build without the GTX 1050 Ti since it's the only GPU that has not sky-rocketed. If he was to get a 1050, then he mind's well get new parts...