List<PriceDetail> prices =
                (from item in xmlDoc.Descendants(shop.DescendantXName)
                 select new PriceDetail
                 {
                     Price = GetPrice(item.Element(shop.PriceXPath).Value),
                     GameVersion = GetGameVersion(((IEnumerable)item.XPathEvaluate(shop.TitleXPath)).Cast<XAttribute>().First<XAttribute>().Value, item.Element(shop.PlatformXPath).Value),
                     Shop = shop,
                     Link = item.Element(shop.LinkXPath).Value,
                     InStock = InStock(item.Element(shop.InStockXPath).Value)
                 }).ToList<PriceDetail>();

((IEnumerable)item.XPathEvaluate(shop.TitleXPath)).Cast<XAttribute>().First<XAttribute>().Value

someXPathExpression

string(someXPathExpression)

string result = item.XPathEvaluate(shop.TitleXPath) as string;

using System;
using System.IO;
using System.Xml.Linq;
using System.Xml.XPath;

class TestXPath
{
    static void Main(string[] args)
    {

        string xml1 =
@"<t>
 <a b='attribute value'/>
 <c>
   <b>element value</b>
 </c>
 <e b='attribute value'/>
</t>";

        string xml2 =
@"<t>
 <c>
   <b>element value</b>
 </c>
 <e b='attribute value'/>
</t>";

        TextReader sr = new StringReader(xml1);
        XDocument xdoc = XDocument.Load(sr, LoadOptions.None);

        string result1 = xdoc.XPathEvaluate("string(/*/*/@b | /*/*/b)") as string;

        TextReader sr2 = new StringReader(xml2);
        XDocument xdoc2 = XDocument.Load(sr2, LoadOptions.None);

        string result2 = xdoc2.XPathEvaluate("string(/*/*/@b | /*/*/b)") as string;

        Console.WriteLine(result1);
        Console.WriteLine(result2);


    }
}

attribute value
element value

XElement e = item as XElement;
XAttribute a = item as XAttribute;

if(e != null)
   //item is of type XElement
else
  //item is of type XAttribute