eBay Price Tracker: How to Monitor Prices Automatically (Alerts, History, and Data Model)

-- watches: the user-defined thing to monitor
CREATE TABLE IF NOT EXISTS watches (
  id INTEGER PRIMARY KEY AUTOINCREMENT,
  query TEXT NOT NULL,
  min_price REAL,
  max_price REAL,
  condition TEXT,
  created_at TEXT NOT NULL
);

-- listings: discovered listings (stable identity)
CREATE TABLE IF NOT EXISTS listings (
  id INTEGER PRIMARY KEY AUTOINCREMENT,
  ebay_listing_id TEXT NOT NULL UNIQUE,
  title TEXT,
  item_url TEXT,
  condition TEXT,
  seller TEXT
);

-- observations: price history over time
CREATE TABLE IF NOT EXISTS observations (
  id INTEGER PRIMARY KEY AUTOINCREMENT,
  listing_id INTEGER NOT NULL,
  observed_at TEXT NOT NULL,
  price REAL,
  shipping REAL,
  currency TEXT,
  total REAL,
  FOREIGN KEY(listing_id) REFERENCES listings(id)
);

CREATE INDEX IF NOT EXISTS idx_obs_listing_time ON observations(listing_id, observed_at);

pip install requests beautifulsoup4 lxml

import time
import random
from typing import Optional

import requests

TIMEOUT = (10, 30)

HEADERS = {
    "User-Agent": (
        "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) "
        "AppleWebKit/537.36 (KHTML, like Gecko) "
        "Chrome/123.0.0.0 Safari/537.36"
    ),
    "Accept": "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8",
    "Accept-Language": "en-US,en;q=0.9",
}

session = requests.Session()


def fetch(url: str, *, proxy_url: Optional[str] = None) -> str:
    proxies = None
    if proxy_url:
        proxies = {"http": proxy_url, "https": proxy_url}

    r = session.get(url, headers=HEADERS, timeout=TIMEOUT, proxies=proxies)

    # eBay may rate-limit; in production you’ll add retries/backoff
    if r.status_code in (429, 503, 500, 502, 504):
        time.sleep(5 + random.random() * 3)
    r.raise_for_status()
    return r.text

import re
from bs4 import BeautifulSoup
from urllib.parse import urlparse, parse_qs


def parse_money(text: str) -> float | None:
    if not text:
        return None
    # supports "US $12.34" or "$12.34"
    m = re.search(r"(\d+[\d,]*\.?\d*)", text.replace(",", ""))
    return float(m.group(1)) if m else None


def extract_listing_id(url: str) -> str | None:
    # Many eBay item URLs contain /itm/<id>
    m = re.search(r"/itm/(?:[^/]+/)?(\d{9,})", url)
    return m.group(1) if m else None


def parse_ebay_search(html: str) -> list[dict]:
    soup = BeautifulSoup(html, "lxml")
    out = []

    for item in soup.select("li.s-item"):
        a = item.select_one("a.s-item__link")
        if not a:
            continue

        url = a.get("href")
        title = (item.select_one("div.s-item__title") or item.select_one("h3.s-item__title"))
        title_text = title.get_text(" ", strip=True) if title else None

        price_el = item.select_one("span.s-item__price")
        ship_el = item.select_one("span.s-item__shipping")

        price = parse_money(price_el.get_text(" ", strip=True) if price_el else "")
        shipping = parse_money(ship_el.get_text(" ", strip=True) if ship_el else "")

        listing_id = extract_listing_id(url or "")
        if not listing_id:
            continue

        out.append({
            "ebay_listing_id": listing_id,
            "title": title_text,
            "item_url": url,
            "price": price,
            "shipping": shipping or 0.0,
            "currency": "USD",  # best-effort default
        })

    return out

from urllib.parse import urlencode

BASE = "https://www.ebay.com/sch/i.html"


def build_search_url(query: str, page: int = 1) -> str:
    qs = urlencode({"_nkw": query, "_pgn": str(page)})
    return f"{BASE}?{qs}"


def crawl_query(query: str, pages: int = 3, proxy_url: str | None = None) -> list[dict]:
    rows = []
    for p in range(1, pages + 1):
        url = build_search_url(query, page=p)
        html = fetch(url, proxy_url=proxy_url)
        batch = parse_ebay_search(html)
        print("page", p, "items", len(batch))

        rows.extend(batch)
        time.sleep(2 + random.random())

        if not batch:
            break

    return rows