rocknbil - 4:02 pm on Jun 8, 2012 (gmt 0)
Context is the key. For a 1-5 products-rarely-changed site, you don't need the overhead of a huge cart with features you'll never use. It's is demanding on resources and file space (most of them are huge) and likely to be slow(er), especially on shared hosting. Any more than that, or frequently changing products requiring modification by the site owner on a regular basis, use an existing solution.
Temper that with budget and experience - if #1, do you have the skills to write a secure script? If the answer is no, or "I can do anything even if it takes me forever to figure it out," there are lightweight solutions you can implement without re-inventing the wheel. Shopify is one good example for a few simple products, but it's a hosted solution.