In a cap-weighted fund, the fund itself isn't buying or selling at all (except to support redemptions or purchases of the fund). As the value of a stock in the index goes up, then its value in the fund goes up naturally. This is the advantage of a cap-weighted fund, that it doesn't have to trade (buy and sell), it just sits on the stocks. That makes a cap-weighted fund inexpensive (low trading costs) and tax-efficient (doesn't trigger capital gains due to sales).
The buying high and selling low referred to by "fundamental indexation" advocates like Wisdom Tree is buying high and selling low on the part of the investor. That is, when you purchase the market-cap-weighted fund, at that time that you purchase, you will spend more on the higher-priced stocks, just because they account for more of the value of the fund, and less money goes to the cheaper stocks which account for less of the value of the fund.
In the prospectus for a fund they should tell you which index they use, and if the prospectus doesn't describe the weighting of the index, you could do a web search for the index name and find out how that index is constructed. A market-cap-weighted fund is the standard kind of weighting which is what you get if you buy the stocks in the index and then hold them without buying or selling.
Most of the famous indexes (e.g. S&P500) are cap-weighted, with the notable exception of the Dow Jones Industrial Average which is "price-weighted" http://en.wikipedia.org/wiki/Price-weighted_index. Price-weighting is just an archaic tradition, not something one would use for a new index design today.
A fund weighted by "fundamentals" or equal-weighted, rather than cap-weighted, is effectively doing a kind of rebalancing, selling what's gone up to buy more of what's gone down. Rather than buying an exotic fund, you could get a similar effect by buying a balanced fund (one that mixes stocks and bonds). Then when stocks go up, your fund would sell them and buy bonds, and the fund would sell the most of the highest-market-cap stocks that make up more of the index. And vice versa of course.
But the fundamental-weighted funds are fine, the more important considerations include your stocks vs. bonds percentages (asset allocation) and whether you make irrational trades instead of sticking to a plan.